screen flashing to black every several seconds

[Claude Jones]

For no explainable reason, my graphic interface has gone crazy. It 
flashes to black for a moment everal several seconds. Nothing else seems 
to be affected. If I'm typing, words keep getting put in the doc. 
Downloads continue, etc... I loaded some of the latest patches/updates 
last night. Apart from that this machine was idle all day. It's up on 
the net with Firestarter providing pretty strict rules. I just tried 
downloading/installing the latest ATI Radeon 9200 video driver from ATI. 
I searched the list for similar behavior, but couldn't find anything. 
What could have changed in my absence??? Have I been hacked by someone?

-- 
Claude Jones
Bluemont, VA, USA