random pc crashes?

i have 2 hard drives,

1st hdd with 2 partitions: an xp partition and a backup partition that i keep all my documents on.

2nd hdd has 1 with vista installed.

lately i will be using the xp partition and after about 1 min it will crash and restart, as though you flipped the switch on the powerstrip off and back on.

very very rarely will this ever happen on my vista partition. but both use the backup partition located on #1.

the way i get it to stop is just opening the computer, moving power cables around or switching them (Basicly just screwing with stuff at this point) and it will be stable for about 3 days, then it starts the crashing again until i screw with it.

i hope my psu isn't dying, but it also might be a hdd. i recently bought it from newegg.

any ideas on what's causing it?

o, ive been through all that. trust me, i know what problems they're talking about.i hav it set up correctly now.

on the evenviewer, does that clear after the shutdown? in other words, do i need to be watching for the error right when it crashes, or will i be able to see it after it boots back up. (it is CRASHING after all, as in,the computer turns OFF which limits the ability of using it whatsoever)

ok, i did some research and found out how to make it not automatically restart when it gets the error. instead it shows me a blue screen with the hexidecimal Stop error. personally i don't know what to do with it. i made a copy of the .dmp file of the error onto a flash drive, but i don't know how to read them. im sure i could figure out a way, but i still wouldn't know what to do with it.

does anyone here know how to debug using a Stop error code?