my motorola e815 has a TF card slot. well i try to put my .mp3s on it and when i put it in the phone they get deleted. it worked before. should i reformat the card? thats what im thinking it is.

Does this happen all the time or just to the cell? Also try to turn the phone off, put the tf in, and then start the phone, I can't be certain why it would do this, possibly a format would help, however be careful, anything that needs to be formatted to work correctly, usually is starting to fail.