ANSWER TO YOUR QUESTIONS:
What happens when you click on MP3 file. - THE APP CLOSES.
Does is play but no sound? - DOES NOT PLAY, NO SOUND, APP CLOSES
Any Error? - NO ERROR, APP CLOSES
Is this related to a specific MP3 file or does the same thing happen with all MP3 files? - HAPPENS FOR ALL MP3 FILES
Do other audio file types work? M4A, AAC? - I ONLY HAVE MP3s, NO OTHER FORMATS
If you still have the preloaded sample Mp3 files do you see the same issue when trying to play those? - I NO LONGER HAVE THE PRELOADED SAMPLES MP3 FILES
Can you upload a sample file and post a link? - https://www.mediafire.com/?gwcdeh38dpx3q71