Manually reinstall the latest firmware. Sometimes the firmware in the player becomes corrupted. Never insert or remove a card while the player is on. Use Sandisk class 4 micro SDHC cards for the best compatibility. Cards faster than class 4 are likely to cause issues.
http://forums.sandisk.com/t5/Sansa-Fuze/Sansa-Fuze-Firmware-Update-01-02-31-amp-02-03-33/td-p/139175
