Thanks for your assistance. Sometime after installing 10-11 drivers
from ATI a Windows update loaded an updated driver
which I think is about the time the issue started. I had installed 10-12 drivers after running the uninstall but the problem persisted. This time ran Driver Sweeper as well, then installed 10-12 and the latest drivers for the ATI tuner card (10-4 I think).
I thought it might have something to do with Zune software going into idle screen saver mode, but it uses GPU hardware acceleration, so most likely ATI driver. If problem persists I will roll back to 10-11 nad stay there.