iCris the only way I know without loosing your data is under the windows OS
First plug in the ipod, go to My Computer. Click on the ipod drive, then go to tools > folder options. Then click view, click show hidden files. Go to ipod_control. Then go to device there should be a file named "_locked" ,delete that. Unplug the ipod and you should be ready to go hope this makes sense, let me know if there is a step that i may have missed. Sorry I do not know about how to do that on the other computer OS :-) Good Luck