Recently my screen image will contract by about 10 to 15 percent, and immediately expand again. This happens several times a day, with no connection to what I'm doing at the time, that I have been able to identify. Once or twice recently the screen went to black, for about one or two seconds, and then the image came back.

My wife suspected that it was caused by power changes from appliance or furnace motor turnings on or off. I personally question this, because I've not been able, when it happened, to detect that the furnace just came on or off. In addition, I do have the computer on a surge suppressor.

The computer is about four years old, which I understand is a relatively old computer. It is a Compaq EVO W-4000 work station, running on XP Pro. Lots of memory, and lots of hard disk space available.

My pure guess (and I can't really tell you why) is that the problem is associated with the monitor rather than the computer, but of course I stand to be corrected.

Does anybody have any sage advice or diagnosis?

Dave Oesterreich