Graphics card glitches, help please?

Recently I have been logging in and seeing strange, corrupted patters across my screen. Then, after a couple seconds, It goes black, and a new, random, corrupted image patterns across the screen. I have to start in safe mode because it basically is unresponsive in normal mode. The reason I think it's my graphics card is because sometimes, if I update graphics drivers, it stops the problem temporarily. This is not the first time I've encountered this problem, and I actually am using a card the manufacturer sent me because they claimed that the other was defective, even though the same problem occurred on the old one. My card is VisionTek Radeon HD 4870, and I am running on Windows 7 64-bit.