Your android headunit boots up, and you select your tunes, and no sound.
One of the worst positions to be in with an android head unit is no sound from the speakers. The thought of a drive without any music is worrying. The Volume is on max and there is still no sound.
Boot, no sound
You can get into a situation where the android part of the android headunit boots up and runs the software but ! The electronics that powers the internal amplifier, the little chip that makes the sounds or your external amplifier needs more power than the android part does to work.
This leads to a strange situation where the android part is able to boot and play the music but the amplifier part of the head unit or even your external amplifier doesn’t enough volts to make the sound happen.
You would typically be in this situation while you are installing your android headunit or maybe showing it off or doing some work on the car. If the vehicle battery is a bit weak or you have left the accessories powered up long enough to drain the battery down a fair bit, you can be in this situation.
The fix for this one
The solution to no sound in this situation would be to get the engine running. The engine alternator will not only have enough energy to charge the battery. It will also enough juice to give your android headunit and even your external amplifier (if there is one) what it needs to produce sounds.
You may find, by this point, your car battery doesn’t have enough volts to turn the starter. If you are going to have to jump start the car, it would be best to pull the head unit fuse. Only while you are boosting the battery.
Not all the ‘no sound’ from the android headunits faults are complicated or require a reboot.