I held Menu and Center button down to put it in disk mode it showed the apple logo for a few seconds then switched back to the normal screen. Any ideas on what the problem could be?
Although I think PaulJam's suspicion that you have a classic and not a 5.5G is probably right - I just thought I'd point out that Menu + Center is not the entire shortcut for getting the iPod into disk mode, that's the key combo for hard reset - you need to follow it up with Play + Center immediately the screen clears after you've done the reset.