Does the voice for your navigation still work? If not it is a bad tuner module.

It is one of only a few things:
1. Bad Nav screen
2. Bad tuner module
3. Bad wiring
4. Dying battery

I haven't experienced the electrical demons other have, but you might want a new battery first. If that doesn't solve it, then go into the secret nav menu and check all the buttons. If the buttons on the nav screen all respond and test ok, then you are down to wiring and tuner module.

Pop the harness off the tuner and check the wires in the middle for power. Oh, and check the tuner fuse!

d-