Depending on the length of time the power was interrupted, your system may require GPS initialization.

If initialization is not necessary, the system proceeds directly to the Startup Confirmation screen.
If the system fails to locate a sufficient number of satellites to locate your position within 10 minutes, the following screen is displayed.

If you are experiencing GPS reception problems:
Center Vent
NOTE: Take care not to scratch the dashboard or its related parts.
Remove these items:
Audio unit, without navigation system
('9-11 models)
Audio unit, with ...
System Initialization
The navigation system must be initialized if
power to the navigation system is
interrupted for any reason (e.g., the
battery was disconnected). ...
USB Flash Drive
...