Source and Preview monitor blank or displaying hidden windows

In Premiere Pro CS4. Seemingly for no reason my source and prview monitors are no longer working. Instead of playing back the media they just display blank or whatever was on screen before changing focus back to CS4. For instance if I went to import a file and the explorer window opened up, once I closed it I would seem remnants of the explorer window where the Source Monitro should be, so it's obviously a glitch.
Not sure why this is happening. I did a clean install of CS4, and even a full restore of the entire Windows OS and the problem persists. Interestingly I can run After Effects and it works just fine.
Any ideas?


Something like this is "usually" a graphics adapter problem
What is your brand/model (nVidia... ATI... ???) and your device driver number?