sad sad sad day

You sir are fucked!

Anyways, had similar problem for my laptop and the motherboard was broken

if the system runs fine for 10 minutes you can eliminate the mainboard or rather a faulty bios. usually if the system boots fine all things are hooked up correctly (anf thats what the mainboard does) and one of them is failing as soon as stressed.
you can also rule out the gfx card (if it doesnt depend on hardware stress, meaning it always crashes after starting a game, also make sure it doesnt overheat which would be rather unlikely and you could also tell by stress testing) but generally symptoms dont sound like gfx card. if it only crashes after playing witcher 2 for 10mins it would be the gfx card but everyone can figure that out so i assume it isnt. (lucky u, thats the most expensive part)
also CPU is rather unlikely cause that would cut out right away or as soon as stressed.
id say its the RAM so try only 1 slot with 1 ram bar at a time and you will find the faulty one. also try booting it but keeping it on standby just to eliminate the stress factor which could be any hardware component and would make trouble shooting a lot harder.

tl:dr cause ur drunk as a bukkit:
try trouble shooting the ram

Try the RAM.

Did you plug all the power connectors in (6-pin GPU connector, additional CPU power, ...)? Your PC might have insufficient power while in load...It's already happened to me a few times.