Yes, I have seen this sort of thing before. As suggested it could be the CRT on the way south...........it could even be the video card memory chips degrading.

What I would do is make sure that the system recognises the screen for what it really is, rather than a generic plug and play monitor, and that you have the display manufacturer's drivers.

After that, my experience has been that it is your refresh rate that causes this.

An experiment:

Start with a refresh rate of 75Hz................. if the problem happens, change it to 72Hz.............. then change it back

You may be using 85Hz, which might be just a fraction too fast?

Also, check that the video card is firmly seated and that its fan (if it has one) is clean and working, and the heatsink is clean.

I actually have a box that doe the exact same thing from time to time......... I change the refresh rate and it resizes itself and works just fine.

The strange thing is that it goes from 85~75~85 or whatever, the actual speed does not seem to matter, just changing the refresh rate works