Diagnosing a failing PC can be an extremely frustrating experience.  What can seem like a relatively harmless problem - maybe an isolated BSOD or a random reboot - can snowball into countless hours of pulling hardware apart and swapping out components in an effort to isolate the source of the problem.  The worst part about this process is that several of the most important components in the system can cause similar problems.  Whether the problem is the CPU, RAM, motherboard, power supply, hard drive, or even the software, the user often doesn't know what is causing the instability without extensive testing.