I've never had that problem after umpteen hundred hours using mine as a player.
I'd rock over to
nomadness.net and see if there's anything in the FAQ or forums about it.
You can update the firmware without sacrificing the content but more likely you'll have to do something more drastic.
Start by going into resue mode and running a Clean Up. This will not erase your data (sort of like running a Defrag.)
After that you may need to move into more drastic steps such as reformatting or reloading the OS. These will obviously wipe your content so Back IT Up!
Good Luck.