Eddie,
I had a problem with my PSR 2000 recently that the Track 1 button stopped working. The indicator light would not turn on. I did a system reset (holding down the far right "C", the last note while turning it on. There were a few things I had to reset to the way I like the keyboard to work but it did not affect my favorites, name, etc. but I backed them up before anyway.

That seemed to fix the problem. Could be just a glitch. Intermittent problems are the hardest to find. If it is the same note each time then it is probably the key switch as the others have mentioned. If it is a different note each time a reset might help it.
Hopefully it will be something that does not cost anything to fix.

Good luck,
- Brian