You will need to set your unit in iBoot and then press the power button and the home for half a minute and then wait for the screen to display "connect to iTunes".
You will now need to restore your iTunes by reinstalling it. Make sure that you backed up before doing this.
If your system still does not work after this, then you will need to bring your device to the nearest Apple Repair Centre since this is a registration issue on their part.
It might take them 2 to 3 days to fix your unit.