My problem (with Curve 8310) is that my MP3 files are for the most part not visible. Anyways, just tried the SIMPLE fix, and worked for me -- remove battery and microSD card for ~15 seconds, then wait.
Notably for others, ONLY the same (only a few) MP3's showed up ... at first, then the list populated with ALL my Mp3's.
So give it a minute, hopefully this'll work for you too.
[Note, I never was experiencing any 'freezing' or crashing, just not being able to see the MP3 files in the Media player on my BB.]