i though i should let you guys know.
after i reset the phone twice yesterday, i just had a same problem again. my phone could not read the mp 3 "audio file" and my phone would not ring it.
so as gratfuldead69 said, i killed? the all the app (advanced task cleaner) now and my phone is reading audio file.
so i think i should buy extended battery too..
hopefully, new battery clear all the problem...
It may have been a corrupt application or corrupt file causing this problem. You can also try to remove each application you think may affect it then re-installl them one at a time.
Hope this helps