Screen goes black when I try to play a game.

I've got a problem with a computer I ordered from iBuyPower.com. I've had the rig for about two weeks now, and as of a few days ago I'm now unable to play any of the games I've got installed. Whenever I try to start Warhammer Online, Age of Conan or Lord of the Rings Online the screen goes black as the game loads, and the first of the pre-game logos usually comes up. Then the screen goes black again, a brief corruption flashes across the screen, and the light on the monitor begins blinking as if it's lost the signal. I can still hear the sounds of the game through my speakers, but the display never comes back...I always have to restart my computer.

Everything works just fine when I'm surfing the web, on my desktop, etc. It's only when I try to play one of my games that this problem occurs. I've asked for help on the IBP forums, and the one answer I received is that my drivers might be out of date. Since then I've downloaded the latest drivers from the ATI website three times, yet the problem persists. I'm really hoping the video card isn't dying already, seeing as how I just paid a thousand bucks for this computer less than a month ago...having it break down now would really kind of piss me off.

Here's the specs on my computer:

PSU- 650 Watt
CPU- Intel Core 2 Duo E8500
MoBo- Asus P5KPL-CM Intel G31 Chipset
Video Card- ATI Radeon HD 4850 1GB
Hard Drive- 500 GB
Mnoitor- LCD Monitor 22" Widescreen TFT LCD Support up to 1080P

If anyone out there knows what might be going on, I'd really appreciate your help with this. I'm almost tearing my hair out.

Sounds like your video card isnt getting enough power to me.

Although now that I look again, I see that the case comes with a built-in 420W power supply. Is there a way to see which of the PSUs my computer is currently using?