my MMC card wont open?

I bought an mp3 player with a removable memory feature, so that i can test the device i took an old 16mb MMC card from my digital camera and replace the photo files with Mp3 files I intalled it on the Mp3 player after a couple of hours of listening i turned it off (i think) put it in the cabinet and went to sleep. the following day I again took it from the cabinet to do further test listening after a few second of play the device just freezed to a stop with power indicator light still on, no response to controls either.....I removed the MMC card from the Mp3 player and placesd it on a card reader in my PC hoping to remove what i assumed a corrupted file in the MMC card, but still I cant open it! the PC just "freezes" whenever i make an action relating to openning the MMC files......i have to remove the card to revive my pc into activity.....What could have happened? Is the Mp3 player defective, is there a fault in my operation of the mp3 player?...can i still fix the MMC card....Im asking this because im planning to buy a 128mb mmc card and i want to know if its wise to use it in that expandable mp3 player again.