your nav crashed.

Make sure:
a) your car battery is good - measure it, get a load test done. Bad car batteries can cause under-voltage and cause all sorts of nav problems.

b) likewise, make sure your alternator is good. Monitor the charging voltage in your instrument cluster - put cluster into test mode, move to the test that shows battery voltage, and observe when driving. Good voltage is around 14.5 voltages. Anything below around 13 is poor.

c) if battery and alternator is good, make sure the map disc is in good order. Make sure it is not scratched and has no fingerprints etc. Try a new (not a copy) map disc. This can make a huge difference. If you only have a copy, try making a new copy on a new CD-R (or DVD, as applicable)

d) if all of the above is good, your nav computer may be faulty. Try swapping it with another car to see if the fault stays with the nav computer.