Computer Crashing during heavy Gaming

I recently built my friend a PC using scrap parts from my old builds. I wanted to get him into PC gaming, so I've shown him Dota, League of Legends, Minecraft, etc, etc.

Anyway, whenever he plays games that aren't graphically intensive, he's completely fine. (Like League of Legends)

But when he plays full 3D games, like Minecraft or Garry's Mod, his computer lasts about 4 minutes before crashing. By crashing, I mean that the monitor says it is receiving no input, and the computer shuts off. No fancy Blue Screen.

I've troubleshot a few things. I've dusted it, because I thought it was overheating and I've put in a new PSU, because I thought his could be faulty. Any ideas?

 

His specs are:

Some AMD mobo and CPU. Nothing special, but nothing that could crash. I've checked temps, and nothing goes out of bounds.

A 250w psu

A nVidia GTX 430

 

As far as I can tell nothing is overheating. And if it was overheating, wouldn't he get BSOD?

GTX 430 Minimum System Power Requirement 300w http://www.geforce.co.uk/hardware/desktop-gpus/geforce-gt-430/specifications

try some new video drivers  first. also  try the gtx in a different pc to make sure there are no problems with the card its self.Then change out the powersupply with a know working one it could be your psu its low quality or on be on its way out the gtx is a low power card like 50watts so it should be able to work with almost any psu. 

250W psu and you wonder why it shuts down..

I know, right? I didn't even know they made ones below 350W.

probably a crappy OEM unit out of a del/gateway...paste outher crappy oem makers name here ect.

250w units are not uncommon in pre made computers.

I will back up everyone else its the PSU, not enough wattage...

Definitely the PSU, best buy sells some el cheapos if you dont have a pc store near by, but yeah, 100% the psu

Thanks everyone. I'll try the new PSU. I was using a 250w because I wanted to be a cheap-ass and not use my 500w in my friend's PC.

A cx430w or a XFX450w are cheap but reasonable power supply's with a 80+ rateing (the XFX is a rebranded seasonic)