the device connected to the imac had received the update with itunes then it said to unplug the device from the imac and...

after the ipod classic 4th update it stayed with the charging image on the screen...the device connected to the imac had received the update with itunes then it said to unplug the device from the imac and put it on the charger but it has been plugged in for a long time and waited in the dock but nothing has changed... how can i fix it