Will not recover from recovery mode.

I have checked the battery with a volt meter - it seems to be fine & holds a charge. When I power on the iPod it gives me the connect to iTunes screen. When I connect to iTunes it says that iPod is in recovery mode & needs to be restored. I accept & it begins the restore process. iPod screen flashes white & restarts showing the apple logo with a pinwheel below. The pinwheel disappears & a horizontal meter to show the progress of the recovery just below the apple logo. Before it registers any progress the iPod resets & iTunes says that an unknown error has occurred (#9). Error number nine states that there is a USB problem. I have tried with other usb cords, other computers, other usb ports - always the same. Any suggestions?