Formatting an MP3 player using Windows is not a good idea -- and most players have a built-in format routine.
Some players will lose capacity dramatically if formatted using a computer.
Where the player will tolerate formatting with Windows, you have to choose FAT rather than NTFS (default for Windows XP). If you have done it NTFS, connect again and do it again choosing FAT this time.
Format the MP3 Player using Fat File System. Although if you have lost your mp3 files and want to recover it then use Stellar Phoenix Photo Recovery . It will recover all your Mp3 files. download the demo version from http://www.photo-recovery-software.com/