Need help trouble shooting!

[Link9286]

I have a problem running some games. Two of them being Far Cry 2 and CS 1.6. When I load them up, they run in the background but my monitor loses it signal from the computer. I believe this is my monitors fault because this happens when I connect two different computers to it.

My Monitor:
Vizio 32'' HDTV 720p, 1366x768, (VX32L)

Rig 1:
Dell with Nvidia 7800GTX
DVI to VGA Adaptar running to monitor

Rig 2:
GTX 280
DVI to VGA Adaptar running to monitor
(When I tried DVI to HDMI Adaptar I get a terrible picture)

Now, what can I do about this?

Thanks in advance!