Just guessing here but I wonder if you have some corrupt mp3s in there. Probably the first thing I would try is copying only some of your files (20 songs or so) to a new directory and pointing MC only to that folder. If it works you might have one or more bad mp3s in your collection (there have been a lot of bad ones lately floating around on p2p networks, for example).
If it doesn't work then you may have a larger problem. Did you try completely uninstalling your previous version(s) before installing the new one? You may want to try again. Have you been having any other problems with other applications locking up? It's possible that you have a hardware issue (RAM, hdd?). And of course there's always the possibility of viruses, adware, etc mucking things up; have you scanned for these lately?
I've never had this exact problem myself so it's a tough one for me. Hopefully someone else who has had similar problems can offer suggestions soon. Operating System (and which service packs you have installed) may be helpful. Might be good to post hardware info as well (like type of hard drive, mobo, RAM etc). Good luck and for heaven's sake don't go back to Musicmatch.