Windows On Mac :: Monitor / Keyboard Deactivated While Gaming

I'm running a Mac Pro with 4GB RAM, 512MB of Video RAM, 2 dual core 2.66GHz processors (or more, not completely sure but I know it's at least 2.66GHz). I recently installed Windows 7 using bootcamp, and so far it has disappointed me by actually being good.... something I'm not used to when dealing with windows. Anyway, the OS runs fine for almost everything with the exception of video games. I've only installed one game on it (Oblivion) but for whatever reason at seemingly random time intervals (only when playing the game) the monitor turns off and can't be turned on without a restart, and the keyboard and mouse can no longer input. I can hear the sound playing fine (in fact on multiple occasions I heard myself being killed), but no video and no input.

I have to restart the computer by forcing a shutdown (holding the power button) in order to get input back. I'm not sure if this issue is strictly windows, as it sometimes happens whenever I play EVE when booted into Mac. I'm fairly confident that it's not my graphics card, because if it were, why would mouse and keyboard functions be disabled? I've tried playing around with the games settings (highest possible settings, disabling HDR/Bloom, low settings, ini tweaks, etc) but it makes no difference on the result. Every time, without fail, the monitor turns off, keyboard and mouse stop working, and I am forced to restart. Again, I'm not sure this is strictly a Windows 7 issue as it has happened before when gaming on my Mac. But on the Mac it's a very rare occurrence, it's happening consistently on the Windows partition.

System Specs:
Mac OS X 10.5.7
Windows 7 Build 7100
2 x 2.66 GHz Dual-Core Intel Xeon
4 GB 667 MHz DDR2 FB-DIMM
ATI Radeon X1900 XT

All drivers up to date on both operating systems.