Put it into restore mode and restore through itunes

did you jailbreak it? If you did then you need to find out if its tethered and if it is, restore and find an untethered one (:

hold the power button for 5 seconds then home and power button for 10 seconds then hold the home button and plug the cord into your ipod and then into the computer and it should recognize it in itunes

Is it untethered or tethered
If its tethered:
Hold the power button for 2 seconds whilst on the boot logo
Then hold the power and the home button, when the screen flashes, after 3 seconds let go of the power button
But continue holding the home button for 12 seconds

Then download the Ipsw for your iOS and device
Then download redsnow
Run redsnow > extras > select Ipsw > point it to the one you downloaded
Go back to the start of red snow > extras > just boot tethered
Put your device into DFU if necessary(redsnow will tell you if you have to)
Wait for it to complete

If its untethered:

Hold the power button for 2 seconds whilst on the boot logo
Then hold the power and the home button, when the screen flashes, after 3 seconds let go of the power button
But continue holding the home button for 12 seconds

Now plug it in and iTunes should detect it in recovery mode
Restore it to a new iPod as you may have problems restoring directly to a backup
You could try if you wanted to though