Is there a problem with my starter?

I have a 1999 Kia sportage 2dr. And for some reason early in the morning when the outside temperature is a little chilly. The car will not start. It will not turn over or even "click." Some times I have to lightly tap on what looks to be the alternator, though it could be the starter, and the car will start normally. Does anyone know why my car does this and what the possible reason could be?