Motorola DROID 4 Getting Started Manual page 11

Tip: In the unlikely event that your device becomes unresponsive, try
a forced reboot—press and hold both Power and the down
volume key for up to 10 seconds.
Warning: Please use only an approved charging accessory to charge
your device. Improper handling of the charging port, as well as the
use of an incompatible charger, may cause damage to your device
and void your warranty.
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