You may have to "Reset" the Unit & continue with "Set Up" to bring the Demo Mode setting up so you can turn the Demo mode off. I suspect when your car was repaired that they had to disengage the battery during service work.
This is the procedure to disable Demo mode, but make sure power saving is turned off first, ok? SRC is the button by the knob in the upper right corner, and the MC is the knob itself.
Let me know if you're successful with that procedure.