1. Check that the memory card is securely installed on the front of the unit.
2. Try a different USB Cable.
3. Plug the device into a different USB Port on your computer.
4. Run windows updates, taking all recommended and optional updates.
5. If you are using a Mac, if OSX Lion is installed, the Messager MP3 unit will be unrecognizable. Use a different computer.
6. Unplug the power and USB cables from the device, then remove the memory card from the front of the unit. Check to see that none of the holes are blocked and none of the pins are bent. Re-insert the card firmly to make sure it's seated and reconnect the device to the power and your computer. Sometimes reseating the memory card fixes the problem.
Try reformatting the Message Mate MP3 card: Formatting the Message Mate MP3 Card