A possible problem with my MSI K9 SLI Platinum?

I have an issue I can't seem to figure out on my own. My computer, after about an hour or so... will have a system failure and restart... it does this randomly... and I can't seem to figure out why. I changed my harddrive's sata power to the normal 4 prong, and it delayed the restart considerably, but I'm still not sure how to completely stop this.

My hardware:
MSI K9 SLI Platinum -Motherboard
64 X2 Athlon Dual Core, 3800 -Processor
6800 256mb Geforce Xtreme -Graphic card
2x 512 Corsair DDR Ram
1gb Wester Digital SATA Hard drive
450 or 500w power supply

I'm running Cool n Quiet, no overclock.
CPU runs around 35ºc

If you have any ideas, or you need more information you can email me, messege me, whatever. Thanks for your help.

~Mofrait

 

Download and run Memtest86+ to check for RAM errors. Let it run for a good few hours and see what it turns up.

 

do you know the make & model of your PSU ?

 

yeah, sorry for the delay, was at class... its an Ultra V Series 500Wat ATX with a 120mm fan

 

well ive never heard of that, but it could be big in the US,

did the PSU come with the case ?
if it did then it's probably crap, check out Big B PSU Sticky cos he's da man with PSU's

 

Nope, it was bought seperately, I'm not sure if its largely used in the US either, I'll check it out.

Currently I'm burning a disc with Cygwin and the BIN Memtest for the problem pc. I'll repost any further info I get. Thanks again.

 

Ultra PSU's aren't great, I wouldn' reccommend them.

 

In Big B's post, he said Ultras are recomended, all except for X-Connect. =-/ I should probably purchase a tester anyway.

 

Ahh okay - maybe I've just read some bad stuff.