The GFI outlet that I have used for 2 years will no longer reset. Could it be worn out already? Is it possible that it has gotten some moisture in it, it is a out door location which does get wet in heavy rains. Should I just replace it and hope for the best?

Your GFI may be damp or shoot but you could actually still have a fault on the line. I'd check the line for a fault first but then GFI are fairly cheap and easy to install. I would recommend a water tight cover for the outlet. I use the large clear plastric covers that allow you to have a plug intoi the outlet and still be water tight.