Ipod Classic 160GB only plays correctly while hooked up to computer and used as a music source in Itunes. If you disconnect it and try using it as a portable player,it will play 3 or 4 songs and then stop. It also seems to try playing songs for 20 seconds

I guess I put my entire question in the subject heading box. My Ipod Classic 160Gb only plays songs as it should if it is hooked up to the computer and used as an Itunes source. When I try to use it as a portable,it will play maybe 3 or 4 songs then stop. It also seems to load a track for 15 or 20 seconds,without outputting any audio and then skips to another song,and so on and so forth. It has been restored twice with no improvement. It also seems to require being reset,once it has been disconnected from Itunes before it even tries to play a song. Very disturbing. This Ipod was purchased second hand and I have no reason to believe there was anything wrong with it before I restored it. Please help!!!