I recall this obscure bug from a long time ago and I think it had something to do with the graphics card settings. Are by chance using an ATI graphics card?

If you would like them to give you more help, they would like to know more about the set-up you are running, posting a debug.err file might be helpful (you need to use a 3rd party site to host and set a link on the forums).

Thanks for the responses, guys. Running a Nvidia Gforce 7600 GS, 512MB. Turn everything off and down, but still had the problem. Have been able to work around it, tho, as it seems editing some video settings brings the graphics back. But it's not consistent. Seems mostly some combination of brightness, contrast and lighting settings (there are two, I believe. one in basic and one in advance) bring it back, but sometimes kind of dark. Again, strange and not 100% predictable, but at least work-able most of the time.