If you had a lot of dust in your case that can really cause a problem. Dust can get in the fans and screw up everything. If that was the case, just be lucky that you didn't hurt anything else.
I'd try what Buzzkill said and if that doesn't work and you do have another slot, take off one of the metal casings on the back and put your card into the other slot. Try that, and if that doesn't work either then your videocard is probably shot. Only thing I can think of right now.
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