When I say overlapping display, its the only really the only way I know how to describe what happens. i wanted to post this weeks ago but I wanted some screen shots of what happens before I ask for help.
How long have you had the card for?
Most GPU's have a 1-3 year warranty so it might be worth investigating that. I would also remove and reseat the GPU. Also, check for updated or newer drivers just to rule software out.