please help!!

Good day, i have a MBoard or maybe a cpu or maybe a GCard issue, not really sure!! i have used AMD's for about 6 years now and the same problem has haunted me during that time.
The systems i build for myself have a habit of RESTARTING themselves!! dosn't matter if i am playing games or writing emails!!
Just pop restart and re-boot windows for no reason!!
Dosn't happen on the systems i build for other people though, funny that

latest incarnation:
as of last week

Abit NF7-s2g
Athlon xp 2800
768 ddr pc2100, about to be Corsair 1G ddr pc3200
GeForce 6600GT 256mb, "xpert vision" cheap one
Creative Audgi, old one
120 gig Barracuda 8m
60 gig Barracuda 3m
XP pro
service pack 2
500w heavy duty PSW (Heavy One)

the virtual memory is set to double my ram 1536mb
the AGP is set to 256mb in the bios
the memory settings are set to standard in the bios
and the Graphic Card is no longer overclocked.

Please help, as this is slowly driving me mad!!!!!

on the side of the box it says Magna ATX 500W (transparent pus w/durl fans.
i would doubt its well known, pirspect top, alli base, fan control at the back, .......

bios is the thing that you press delete or f2 or whatever your computer says. rails is the voltage of your power supply ex +12, +5

(\__/)
(='.'=)
(" )_(" ) bunny pwns j00

here is something that will help you go to system properties go to the advanced tab click on startup and recovery then uncheck the bok that says automatically restart. this will stop the computer from automatically
restarting on an error. instead you will probably get an error screen that can tell you what the problem could be (you might have to search up the error code on google or something) for more details

hope this helps