Video Crash

Hiyas,

I've been experiencing a crash that I've never seen before:

Specs:
Amd Athlon 1700+ on MSI KT3 Ultra 2ce
Windows XP SP2 (Updated from SP1 after crash started)
768mb pc2700 (Upgraded from 256mb pc2700 after crash started)
Gainward geForce Ti 4200

Description:
My system has worked fine for about a year. Over the past 3 weeks, every time I try to run any kind of game, it has given me a black screen. The monitor goes into sleep mode, and refuses to speak with the pc at all. I can turn the monitor back on, but I only get a "no signal" message. Now, I've run games on this exact setup for the past year with no problems, the same games I'm trying to run now. I can run Photoshop just fine, and I can browse around the web, or anything else. But when I try to run a game, either immediately, or within about 20 minutes, the screen goes black, and into sleep mode.

Things I've done since this problem started:
Updated all relevant drivers (in some cases multiple times): Chipset, Vid Card, Monitor. (Uninstalled the old ones first.)
Did all the windows updates, including SP2.
Upgraded to directx 9.0c
Tested RAM with Memtest86 (Passed)
Bought and installed more RAM.
Scoured the net for clues.

Nothing has worked!

Could this be a BIOS issue? I've read that sometimes updating windows will cause an old BIOS problems with video, and I've never flashed mine. I really don't want to do it if I don't have to.

Is my video card broken even though it runs everything other than games just fine?

Could there be a bad sector in my page file? If so, how do I test for that?