How to unblock electrically my macbook pro?

- Try a new cable.

- Inspect the dock connector on the iPod for bent or missing contacts, foreign material, corroded contacts, broken, missing or cracked plastic.

- Try on another computer to help determine if computer or iPod problem

- Make an appointment at the Genius Bar of an Apple store.

http://www.apple.com/retail/geniusbar/

On your Mac ....

Reset the PRAM > How to Reset NVRAM on your Mac - Apple Support

If that doesn't help, reset the SMC > Reset the System Management Controller (SMC) on your Mac - Apple Support