It shouldn't make a difference, but have you tried reverting to he stock BB kernel and seeing if it works? If it does, it's the kernel - if not, then at least you've eliminated one of the variables.
Another thought - do you have a lot of music on the phone (SDCard)? if so, might want to check and see if you have a lot of temp library files built up that are making it hard for it to scan for music. The best thing in this case would be to remove them - however, that can be a chore in and of itself. Might be easier to downlaod SDREscan from Market (or another rescanning app) and rescan your entire collection, and then try running the Music app again.