New build Problems

[Che Roriniho]

Hi there, New on this bit of the forum, so g'morning.

I recently built a new computer, and the building itself went almost perfectly, so no problems there as far as I know. Here's my rig:

Q6600 (with after m arket AC fan)
8800GT 512MB (from BFG)
500GB HDD
700W Arctic Cooling PSU
MSI P45 Neo-F Mobo
4GB OCZ 800MHz DDR2 RAM
Vista 64bit SP1
CM 690 case

and I think that's all.

The problem is is that it keeps crashing. Not programs crashing, so that I can Ctrl-alt-del out of them, but proper crashing. Even my caps, num, and scroll lock buttons on my keyboard works, nothing.

It usually, afaict, happens either when it's left on screensaver for a while (about 20 mins), or when I' playing a game. At first, I thought it was the game at faul, but it has since occured on my desktop, when only Steam and uTorrent was on.

I really really really would like some help here, because I'm starting to feel as if I've wasted the best part of £600, for something that is barely better than my preious rig.

EDIT: I also occasionally, and inexplicably, disconnect from the net. Not locally, but just from the nternet. Is this a problem my end, or witht the router?