Sounds like you checked it out pretty thoroughly. Sure sounds like the card is dead to me. I had mine die, but I had a lifetime warranty so it wasn't too big of a deal (I had my replacement die, as well. Second replacement worked until I bought a 570). Seems like these cards have been failing frequently as of late. Only other thing you can do is try plugging your GX2 into someone elses machine and see if it works. My bet it it prob won't.
Unless you have a warranty I don't think getting it fixed it feasible. Even if someone did offer that kind of service it would prob cost more than a new card would be worth. You could always try ebay or something to check for cheaper used cards. Sorry about your bad luck.