I have seen this before, if the GPU has not been damaged by overheating, it is possible to repair this issue. The first thing to check is the GPU fan and insure that it is spinning and not frozen, if it is spinning, use section F
in this Tutorial
on cleaning the inside of your PC. If the fan is frozen in place, and will not rotate, there are several companies that manufacture after market GPU coolers. This is an example.
Of course, a new video card will solve the problem, and the cooler may not if the gpu is damaged. My advice would be to get a new video card if the cleaning does not fix the problem or if the fan is frozen.