More About Points »
Could be your starter if it never starts the engine, otherwise, I can't tell from only this information.
certain vehicles have a manual reverse, where its not even apart of the actual transmission, so that depends (if you want to get it fixed. I did the same exact thing in my old Saturn, I never got it fixed (usually don't need to if you don't want to), just be very careful about parking locations - don't park somewhere that you'll need to go reverse).
you might need a new compressor, I needed a new one on mine about 3 months ago (2001 Infiniti Qx4, 78,000 miles)