prv acting up

Am if anything a noobie to using the PRV. I just learned that I can do it by the track instead of full screen for some options. I have 3 midi tracks with data.. and I was editing one of them in the track view prv, and all of a sudden 2 of the tracks, the volume went to almost zero.. .don't know what I touched or clicked.. but nothing I do brings the volume back up.. I have tried increaseing the velocity up to 95.. has no effect.. help please.