Breaking Down the Boot Process

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Breaking Down the Boot Process

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When a computer fails to boot, this means there is something wrong somewhere in the computer.  We all know this, but where the issue lies can sometimes be hard for the average consumer to explain.  That’s ok though, because in this article we are going to explain the boot process to you and explain a little bit about what is happening and how to describe what you are experiencing to a technician.

For the most part, laptops and desktops power on the same, regardless of you using a Windows or a Mac.  The biggest difference here is that a laptop has a battery, and a desktop does not.  With the release of Windows 8, however, some of the boot up process has been condensed, and therefore you may not get all of these steps as describer.  But we promise you they are still occurring.

When the power is applied

Once you press the power button, only one thing is happening:  the power supply sends power to the rest of the computer.  All of the components begin to come to life such as the hard drive, CPU, RAM, motherboard, etc.  This is the easiest to describe; either things get power or they don’t.  But this doesn’t mean it is the easiest to troubleshoot.  From a technicians perspective, there is a lot of things going on.  The Power Button could be broken, the motherboard could be fried, and something could be shorting the power supply.  Even a bad power cable can prevent power from getting to the computer.  So what are you to do yourself to try and figure it out?


If you are having this issue with a desktop, start with following the power cable.  The power cable should be firmly, not forcefully, seated in the power socket of the computer. If your mains power lead is plugged into a extension cable, ensure that this is plugged in and turned on as well. The extension lead could have been turned off, a cable knocked loose, etc.  If the extension lead has lights on it, are the lights illuminated?  Is anything else plugged in to that extension  that isn’t getting power either, such as a monitor, printer or speakers?  After checking to make sure your computer is properly plugged in to power, try the power button again.  Do you hear anything or see anything?  If you don’t, don’t worry.  The next step is to use  your nose.  Do you smell anything that smells burnt.  If you smell something that smells burnt, unplug the computer completely and give us a call.  DO NOT CONTINUE WITH THIS ON YOUR OWN.  DO NOT KEEP ATTEMPTING TO POWER UP YOUR COMPUTER!

If you don’t smell or see anything, then chances are the power supply or the motherboard is simply malfunctioning.

For laptop computers, start by removing the power cord from the DC jack, while leaving the battery in, try to power the computer on again.  If this doesn’t work, remove the battery and reconnect the power cord and again try to power it on.  If this has resulted in nothing, sniff around the vents for anything that smells burnt.  Because it is a laptop, keep in mind that they get a lot hotter than desktops due to the confined space.  This can throw off many of noses.   You are smelling out something that specifically smells like burning plastic.

POST, it’s not just a cereal

Once power begins to flow through the computer, lights will come on, fans will spin.  The other thing that occurs, is this is when beep or light codes come in to the picture.  The BIOS, a small chip in the computer that gets the computer going, performs a Power-On Self-Test (POST) that makes sure all the hardware is working properly using a whole bunch of simple math.  Beep or light sequences can signal a hardware failure.  Note that not all computers beep, but as long as the computer continues to boot, then there is nothing to worry about.  Many computers also have a single beep to let you know that everything is fine as well.

If your computer powers on with lights on the computer coming up, and fans spinning but nothing on the display, we know the issue lies with hardware.  Why?  Because this is all POST does, it tests for hardware, and not software.  A failure to post can be the result of a bad CPU, BIOS chip, RAM or a Motherboard.  This is a small limited list of what could be wrong, and  is all a technician needs to start seeing what could be the problem.

If your computer posts, but does not continue to boot, then chances are the POST missed something (usually unlikely), or your video card/graphics processor lied to your BIOS about working properly.

If you hear various beeping coming from your computer, try to count the number of beeps.  Many computers will also repeat beep sequences, in an attempt to make sure you get them down.  Consult with either a technician or the manufacturer of your computer to figure out what the beep code is.  If your computer never beeps, and still isn’t beeping, looking for blinking lights on the computer (usually refers to only laptops).  Remember, at this point, it is all still hardware based.

BIOS takes over

Your computer’s BIOS chip is very important.  It does a lot of different things not just when the computer is power on, but while it is on as well.  It monitors voltages, temperatures, things being plugged in, etc.  It’s very important for such a small little chip.  After POST is when the BIOS chip really starts putting everyone to work.  Your screen should come alive and display things like the manufacturer, BIOS manufacturer, the amount of RAM installed, processor specs, drives detected, etc.  Many computers, especially those running Windows 8, with a quick splash screen showing the manufacturers logo.  This process is generally really quick, and goes without error.

Once the BIOS is done looking at all the different pieces of hardware, it is going to try and grab the hard drive with the operating system installed.  This is when BIOS attempts to hand over the computers operation over to the operating system.  If the BIOS can’t find a hard drive, it will let you know saying things like no drive detected.  If the BIOS finds a hard drive, but not an operating system, it will let you know this as well.  Please keep in mind that there is a boot device order in every computer.  Most commonly, the BIOS will first look for an operating system on a hard drive disk, then either a CD/DVD or USB device.  If none of those have an operating system, or the operating system is on a device that is malfunctioning, then your BIOS will report the message accordingly.

If your BIOS is saying there is no disk found, this typically means that either the controller that controls the hard drive is bad, or the hard drive itself is bad.  And the boot process will not know the difference.  If your computer finds the disk, but not the operating system, typically a message reading “Operating System Not Found” is displayed on the screen.  This can be the result of a bad hard drive.

After the operating system has been found, your BIOS is going to begin loading the “boot loader” in to your computers RAM.  This is where our list of possible issues begin to grow again.  If the RAM is bad, things like checksum failures can occur.  If the hard drive is bad, nothing will happen.  If the boot loader is bad, nothing will happen.  If the operating system is bad, we may or may not see anything.  It all gets a little crazy at this point inside the computer; think of it as a shift change when half the staff is going home and the oncoming staff is coming on.  The ones going home have quit for the day, leaving all the problems (known and not known) to the next shift.

The operating system takes over

Up to now, everything has been all about the hardware working properly.  The boot loader is the only piece of software that is now running, it’s only job and thing it knows how to do is find the operating system and load it in to the computer’s memory (or RAM).  Once the boot loader has completed its task in loading the operating system, it hands over control and unloads itself.

The operating systems first task is to go back to the hardware and begin loading various pieces of software based on the hardware that it was told is on the computer.  If any of these pieces of software, called Drivers, are bad, you can get various errors to include the blue screen of death.  This can narrow down the list to what is wrong, but not necessarily if it is hardware related or software related.  If a driver loaded incorrectly, like making a left turn instead of a right, you can get an error.  If the hardware is to blame, the same thing will occur.  There are one of three things you will see on your display:

1)  The Windows or Operating System Logo, this means the operating system is loading.

2)  An error screen, which means something went wrong.  Copy as much error information as you can.

2a) A BSOD (Blue Screen Of Death) may appear on screen.  Please make a note of the error details, and the error code.  Technicians ideally need both of these details to help you quicker.

It will look something akin to BAD_POOL_HEADER  Stop code: 0x00000019: The last 2 numbers (in this case 19), are what the technician requires.

3)  Nothing can display, which means there is something wrong with the graphics processor, the operating system, a driver, etc.

If your computer displays the operating system logo, and then reboots immediately, this means one of two things:  the operating system is corrupted and there is no error to display, or there is a power related issue.  Other things could be wrong as well, but this is where your technician will start looking if your computer has problems at this time.

If your computer gets through this little bit, the first thing it will do is finish installing any updates that requires a minimal amount of the operating system loaded in order to install.  It is very critical to not turn off or even reboot your computer at this time.  Think of it as keeping track of a bunch of loose papers on a windy day.  If you power off the computer or reboot it, you run the risk of the computer throwing those paper in the air and saying “forget this…” and your operating system becoming corrupted.  At the same time, if your computer is taking too long trying to install these updates (such as more than an hour or two), something is wrong with the updates, the operating system or the RAM in most cases.  This is bad, because in these cases there is a high risk of losing the operating system.  Don’t panic though, this doesn’t mean you’re at risk of losing your data.  When explaining this to the technician, simply explain that the update process at boot is taking an unusually long time to complete.

If all of this goes well, you will end the majority of the boot process at the login screen.  If you have configured your computer to automatically login, then you will move on the last stage of the boot up process.

After the login process

The login screen is considered a pause for the operating system.  Background tasks specific to the computer in general will have started at this point, and most issues will be related to the software on your computer at this point.  Hardware related issues can still occur, but these should all be followed up with either an error screen, error message, or the computer just powers off or restarts in the case of power related problems and overheating.  To a computer, this has been a long road.  For you, it’s been about 30 seconds.

Once you get to your desktop after logging in, the computer now has to finish loading a few more things.  Most of what is going to be loaded is going to be user specific.  There may be some general computer software that needs to still be loaded, but not that much.  Once you login, depending what you have installed plays an important part to how fast this goes and what can be expected.  If you have a lot of programs installed and configured to load or start when the computer is booted or you login, your computer can take a while to complete this task.  If you experience a long slow period after logging in to your computer, this can be the result of having too much trying to start up all at once.  If you have a mile long taskbar at the bottom right of your windows computer, disable any programs you don’t need, and configure them to not boot up when the computer turns on.  When in doubt about what the program is, contact your technician for further guidance.

Computers running the bare minimum amount of RAM will also run poorly during this step.  It is recommended to have at least 4GB of RAM for Windows Vista, and 6GB of RAM for Windows 7 and 8 to run smoothly during the login process.

Software related issues that are not related to the operating system will display their error messages in the form of a popup window or balloon on the screen.  Pay careful attention to what these say, as they should relate to the program and the problem encountered.

From this point on, issues can arise from either software or hardware.  Paying attention to errors messages that display on your screen will assist you in explaining the problem to the technician.  The more details you can provide, the better at narrowing down the issue becomes.


Guest post by Frederick at Phoenix Computer Hospital.

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