You should be able to force disk mode. In disk mode you can restore the Ipod (either manually, or using Itunes). If that's not possible my guess would be a broken hard drive.
Uninstalling the Rockbox bootloader doesn't cause the behaviour you described, you'd only end up in the Ipod only booting the Apple firmware. So either you need to try harder in forcing disk mode (that will *always* be possible but sometimes it's a bit tricky) or you have a hardware issue.