Searching for new music
Take the memory card out, clean the contacts and if you have an air duster clean the socket, reset the device by doing the following;
take the battery out, hold the power-on button for 30 seconds (time it as it will seem to take forever). Put a new battery in and try it again.
If this is no help then it would seem that either the memory card's file system or the internal memory's file system so plug the device in over USB and backup any data your PC can find. with anything that can be rescued, rescued format the memory using FAT32, do not use quick format.
Alternatively you can buy rescue software from SanDisk www.lc-tech.com/software/rescueprodetail.html but it's not guaranteed to help.