I've played around and built three MCE boxes this year, and all three had the
same problem -- black screen with full MCE window -- with TV out at one time
or another. One also had problems with a DVI-connected DLP projector.
The problem is NOT specific to ATI drivers, as I have found it with the
latest on-board Intel Extreme Graphics 945 chipsets and drivers, and others
see it with Nvidia product.
I'm not sure what makes it go away, but if I throw everything at it,
eventually it does...
-- use the latest drivers
-- switch between full screen and windowed (Alt - Enter) with MC goes black
-- change resolutions within Media Center... for some reason INCREASING
resolution helped me.
-- tell Media Center that the monitor is connected via VGA cable, even if
you're using S-video or composite
-- Burnt offerings to the computer gods seem to help too, old power
supplies and mechanical mice produce lots of smoke and are no great loss.
-- Harass the Microsofties.... I see quite a few similar messages going back
years and yet the problem remains.