Intermittent Hardware Issue

I'm usually one dishing out help on this forum, but I have an issue that I need help with now.

Firstly, I'm 99.9% certain that it's not a software problem of any kind... but rather a hardware problem. I have reinstalled Windows XP for the 1st time 5 times... I've reformatted, I've ran scan disk, defrag and all that jazz. Now here's the problem....

At any given time my computer will simply lock up. Doesn't matter what I am doing, if anything. Doesn't matter what is running. Sometimes it will lock up over and over within minutes. Sometimes it will go a few days without locking up at all. Sometimes it even locks up during boot up. No error messages ever... just locks up... screen frozen. Ctrl-Alt-Delete = nothing. ESC = nothing. F5 = nothing. My only recourse is to hit the "reset" button on the box. Now, here comes the really tricky part... If I power the system down... it will not start up again until I jiggle the power connection to the C drive literally. And sometimes I have to do it a few times... then hit the power button on the box and it will start. Now, when it doesn't start... I get nothing... except the power supply. No beeps, no bios, nothing ... zippo. Just a black screen. I can't recall if the fan on the CPU starts up. Just the power light shows on the box, no hard drive activity.

I'm trying to determine if the problem is with my motherboard or my hard drive or possibly even the IDE port in which it is connected to on the motherboard. Should I try switching the IDE ports and see what I get?

Any thoughts please? Eggs?

Donna