Try Resetting the iPod
- After charging till full charge, at least 2 hours (preferably 4 hours)
- Toggle the Hold switch, make sure you dont see the red mark when you do the next step
- Reset the iPod -> Press Menu and Center button simultaneously for about 10 secs or till the Apple Logo comes ON
- Then release the buttons
- Select your preferred language.
Here is the Apple support Article on the 5Rs
If the above doesn't work, it could be the earphone jack has been shorted, or clogged up and putting the Dock also in mute. This maybe repaired by 3rd Party iPod service.
Have a nice day!