Is My Video Card Going Bad?

Problem: When there is a stationary pic on my screen it is loaded with multi colored square dots. Sometime they flicker sometimes they don't. At times there are a lot of dots, but when I change screens they are sometimes reduced. There seems to be a pattern, but it changes. When I have a moving pic, like a movie, there are no dots within the movie, but they are there on the back screen edge if I don't go full screen. (PS, it's not my monitor.) This is the clincher, every so often the video card will reset itself and the screen goes black for a few seconds and when it comes back on there are no dots for awhile (but they come back).

Before I spend $300 on a new card I need to know it is the problem. I have a ATI Radeon HD 5900 Series video board, but it is 5 years old. I have kept the drivers up to date and the inside of my computer is clean (no dust bunnies on the fans or hardware).

If it is the card, what one do you recommend? I like gaming and playing downloaded HD videos/movies. Thanks in advance for your help.