Q: i was going to update my ipod 4th genertion and now it doeesnt turn on

Try:                           

- iOS: Not responding or does not turn on

- Also try DFU mode after try recovery mode

How to put iPod touch / iPhone into DFU mode « Karthik's scribblings

- If not successful and you can't fully turn the iOS device fully off, let the battery fully drain. After charging for an least an hour try the above again.

- Try another cable

- Try on another computer                            

- If still not successful that usually indicates a hardware problem and an appointment at the Genius Bar of an Apple store is in order.

  Apple Retail Store - Genius Bar