Scrambled Display Vista nVidia

I am having a problem with a scrambled display in Vista. Here's what's
happening:

If the computer has been idle long enough for the display to go into
standby mode, once it is reawakened, everything seems normal. That is,
until you do something that requires UAC, or a 3D game. When the UAC
screen dimms, the screen becomes totally scrambled. The same if you
start a 3D game like Doom. There is no clearing the display - the
computer has to be rebooted.

Interestingly, if after the computer wakes from standby I log off, then
log back on, the system performs properly, with no screen scrambling.

The system is an Athlon X2 6000, nVidia 7900GT, Vista Ultimate (32-bit)
with all the updates and patches. I have installed the nVidia 169.25
drivers, though this problem has existed with all the previous drivers.

Has anyone else had this problem? Has anyone found a solution?

Thanks for your feedback.