My car does this once every so often (drives me crazy). But most often just the screen flips up but no video. The Radio still works but when I press one of the buttons the Nav screen would fluctuate back and forth. When this happens I just force the screen down, then either press the left radio knob in to turn the radio off then press it again to turn the radio on. or after forcing the screen down, i press the screen switch button( the one next to the phone/info button).

Usually that fixes it, or just turn the car off and then turn the car on.