It is possible that your iPod's hard drive has become faulty.
You can try putting it into Disk Mode
If that works, connect it to your computer and run iTunes. If iTunes is able to access the iPod in "recover," it may prompt you to do a Restore, which will erase the iPod, re-install its software, and set it to default settings.
If the iPod does not go into Disk Mode, it is likely that the cause is a faulty hard drive.