A reset can be performed which will recover the unit and allow it to boot.

First hold the power button on top of the unit for about 4 seconds to force a shut down.

Next, hold down the Home button on the front of the unit and push the power button while still holding the Home button.  You can let go of the power button on top as it boots up, but continue to hold down the home button.  The unit will show the splash screen again, then after a few seconds it will go to the white calibration screen.

At this point you can let go of the home button.  Perform the calibration according to the on-screen instructions by tapping and holding in the center of the target as it moves around the screen.  When the calibration is complete, you will be directed to the driver login screen.