Nano 5G ok to disconnect whle in restore progress

hey guys, i have an ipod nano 5G 8GB, my problem is, after i update it for new songs, it appears no song, and then, When iformat it using windows, it tells i neet to restore it using itunes, so i restore it using itunes, the problem is during the restore progress it automatically disconnects itself from the drive saying 'ok to disconnect', and the the restoration stops. and in pc saying "unable to restore, an unidentified problem occur" s0mething like that, please help me, till n0w i cant restore pod. a hjelp will apprciated. tnx in advance.