"stuck" notes

Hi, I'm hoping this is an easy fix. I've formatted an older computer I have and loaded Win XP on it. I want to use it excluseively for music editing. It was working fine when I had Win ME on it but now there is a problem with pro audio 9.
The computer is a P3 200 Mhz, good enough to run Cakewalk. It has an Ensonique VIVO sound card. Anyway, not even connected to a keyboard, just trying to play back a Cakewalk file it sounds as if notes are stuck. I have to reset the midi source to stop it. I think I had this problem years ago but resolved it. Of course, I don't remember what I did. I'm all ears if you have advice. Thank you very much, I'm itchin to start writing.
Best Regards,
Cosmo