Hello, I hope the following is of assistance.
This will be due to a concern with the Bluetooth Voice Control (BVC) module. If the module detects a voltage surge that can damage it then it will shut down to protect itself if this is the case then it needs to reset.
First try having the radio on and press and hold the on off button, the unit will turn off, go blank and then reboot, this can sometimes reboot the BVC module.
If not then the easiest way to reset the module if you have your audio code is to disconnect the car battery for a few minutes.
If neither of these options work then check the power and earth to the BVC module, to get to the module you need to remove the glovebox and the module is bolted to the metal cross beam behind the dash, if the power and earth to the module is OK then unfortunately the module will need replacing, a new module will need programming to the car.
I hope this helps but if you have further questions regarding this let me know and I'll reply as soon as I'm able to.