Need Help on New PC build

Hey Everyone, I'm new around here, but I've been on this site/forum a lot, and it's pretty helpful!

So I need some help...

I've just finished building my new desktop recently and everything seemed to be working fine...

However, to kick things off, I decided to run Crysis...
Things seem to be working pretty fine, but then my monitor would eventually go into standby mode before I could reach the first cut-scene and I can still hear as though things are working fine, but the screen is blank(black). Checking my numlock lights and what not.. it'll be fine for about a minute until it actually freezes up, and the only way to get out of it is a reboot.

I did this test a couple times and still, no solution. It also occured mutliple times in TF2.

I thought it might've been because I have my monitor hooked up to my video card w/ a VGA adapter, since my monitor is old and doesnt take DVI.

To check this, I switched out my monitor w/ my housemate's HDTV. Using a DVI (from vidcard) to HDMI(hdtv).

This seemed to fix the problem with TF2, but Crysis is still giving me the same problem. (the TV says, no signal).

Already checked my temps and what not both for the CPU and GPU.
CPU is in the 40s
GPU is low 60's (which i hear is normal)

Here are my specs:

EVGA 780i mobo
Intel Q9450
Evga 9800GTX
4GB memory
Vista Ultimate 64bit
Corsair 620W PSU

Any solutions you guys can think of?

EDIT: Ran TF2 a few more times.. getting the same problem...

I have other games but I haven't bothered installing them yet. I'll try installing them and I'll post what happens.

I do have the latest drivers, for both the mobo and video card. (and everything else)

I haven't done any OC'ing my self, but I believe the video card was superclocked(?) when I bought it.

Here is the link to the exact card I bought.

http://www.newegg.com/Product/Prod [...] 6814130349

Again, I'll try installing some other games, and see what happens.

Edit: Just installed Guilty Gear XX #Reload (it's a 2D Fighting game).. played for a bit and it still crashed.