Battery was replaced by BMW dealer. The red light on eject button on the nav unit blinks red (i do not have a nav cd in the computer). The radio plays for about 30 seconds (no radio screen comes on) and then shuts off. If you turn if off and then on again, it plays for another 30 seconds. The red triangle light for the radio comes on, but not the red triangle light for the monitor/nav knob. Which would I replace first and is there a place to buy a used one?

Thanks in advance for any advice!