Two computers that I service now have the same problem:
2 small black boxes will flash across the screen about once a minute.
Here are the specifics.
-The boxes are about 1/2" square on a 17" monitor.
-The timing of when they occur is slightly variable but average about once per minute.
-The location of the boxes is the same on both computers and is the exact same spot each time they appear: top box is in the upper 1/3rd of the screen about 1/3rd from left to right; bottom box is in the lower 1/3rd of the screen about 1/3rd from right to left.
-Both computers are running windows 7 professional
-The computers are otherwise different, one is windows 7 64 bit, the other 32 bit; both are different brands, processors, different display adapters
-The bottom box appears a split second before the top box and they both disappear at the same time, a fraction of a second later (it's almost a flash on and off)