Your Computer's Boot-Up Sequence
First off, know your computer's boot-up sequence. I can't stress this enough. By knowing this sequence, the files, drivers and devices that are loaded, and when they're loaded, you can use the information to resolve many problems.
When the computer is first turned on,
the system performs a Power-On Self Test (POST) and starts the actual
BIOS routine. For more information on the BIOS routine,
Near the end of its routine, the BIOS looks for the master boot record (MBR), which contains information on how to locate the bootable drive and the system file 'IO.SYS'.
If any problems are encountered before this, then you know that it is hardware related. In some cases, you can find and repair problems by searching for poor connections, damaged cables, seized fans and power problems. Check that adapter cards and SIMMs or DIMMs are installed in their respective slots properly.
In extreme cases, you may have to strip the computer down to its motherboard, RAM, video card, power supply and CPU. By adding the rest of the devices individually and restarting after each one, you can sometimes discover the problem.
Once the operating system is loaded and takes over the boot-up process you can use the Start-Up menu to control which files and devices are loaded. This is sometimes called a 'Clean Boot'. More on this later. First you should get to know some files.