Your PSU should be fine. Have you tried completely uninstalling the AMD drivers (Use CCleaner to uninstall then do a registry clean to get out any entries in there). Reinstall the latest drivers. If that is still a no go, then it looks like your GPU is failing.
I don't know your location but here is one that I would go with no matter your budget.Video Card: Gigabyte Radeon HD 7770 1GB Video Card
($114.98 @ SuperBiiz)