URGENT! HELP!.Unusual ipod cable Problem?

I have an Ipod..It is 3 yrs old and still in perfect condition..I have a portable charger for it. whenever I connect my cable to the charger and charge ipod..ipod charges perfectly..but if I try to connect to my pc for syncing etc..it does not connect..my pc makes a beep sound like it makes whenevr a device is conected but my ipod doesnt show or charge..i thght cable prob..i have brough 3 brand new cables and tried..but still no luck..charges with the charger but not with pc..i thght it may b my port.but if I connect pendrive or hard disk or an other device it works perfectly.. I even bought a 4 port hub..it also reads evrything except ipod..please hellp..

try system restoring your ipod

First make a backup upgrade to the latest version and the restore it.It should work properly.