Failure to draw popup windows or applications after minimization

[Temlakos]

Why is it, that after two hours of operation, suddenly popup windows 
appear all black? Even Kickstart does this, which means I have a tough 
time even shutting it down. And if I have minimized an application and 
want to come back to it, forget it. Total, unrelieved black. The 
functions are still there, but if I can't see what I'm doing, I can't 
use the mouse.

Even the latest updates did not clear this problem.

Where might the fault lie?

Temlakos