NVIDIA GeForce 7950 GX2 Issue

I can tell you that if the little box is well formed and clean that isn't just a box of different colored pixels then it is software and not your card. OS bugs and drivers but rarely is it hardware. To make sure just post a picture of what it is that you are seeing so that can be ruled out as either software or hardware issue. Random blocks and dots are usually hardware.

Thanks for your response. When the computer first boots up, the "block" is not present. If I open any application (typically Photoshop, Pro Tools or Sony Vegas) the "block" seems to appear transparent, and may display text or a small part of a photograph that was on the previous screen. I initially thought it might be hardware related, and it only happens after the computer (and monitors) heated up. But after going through some tests where I checked immediately after booting up, it still appears. I have an ocean scene as a desktop image, and sometimes I can start Vegas and the "block" will have a "window" displaying part of the ocean photo on my desktop. And, if I move the window, I still get the same "block" - with the same transparent image - that duplicates the position of the original window.
Do you think updated drivers might offer a solution?

It is worth a shot but keep a close but careful eye on that card. I got the older version and they do get hot when not maintained. Drivers for these cards have never been stellar.