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:
Map Coverage
The navigation system provides map
coverage for the contiguous United States,
Alaska, Hawaii, Canada, and Puerto Rico.
The map coverage consists of accurately
mapped (verified) metropolitan area ...
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). ...
Malfunction Indicator Lamp
If this indicator comes on while driving, it means one of the engine’s emissions
control systems may have a problem. Even though you may feel no difference in your
vehicle’s performance, it ...