Wow, a Ti4600. I used to have one of those!! Great card. Hmm, do you're saying you get flashing dots everywhere? Like green and red? Or are they patches of textures that are flashing? That may be artifacting, caused by overheating. I'd first check to make sure the heatsink and fan is still attached properly. And make sure the fan is working, if it isn't, the card is probably overheating and causing the artifacting.
Then I'd try a different driver. Maybe an older one. Maybe even the one that came with the card originally on the driver cd?
Hope this helps a little.