What is recorded on the track? Generally you don't pan stereo tracks - since they are stereo they, in essence, are already "panned."
For example, if you record a piano in stereo (e.g., lower keys to the left and higher keys to the right) and you pan the track hard left, you will end up just getting the left track (i.e., the lower keys) and not the entire piano panned left.
Panning simoly determines how much of the signal comes from each speaker. When you pan hard left you get 100% of the signal from the left speaker. When you pan center you get equal volumes from both left and right speakers. On a mono track, hard left panning will make it sound like the instrument has been placed to the left. On a stereo track it means you will get only whatever is on the left track.
Depending on what is on your track, you might want to convert it to mono. You'll have a lot easier time trying to pan it.