No sound on radio or navigation

Hello I have a toyota prius 2007, recently I took my car to the mechanic (to fix the abs) when I got the car my radio, navigation had no sound... I tried pressing the buttons underneath the screen, the touch screen button and the ones on the steering wheel and nothing seemed to work... while I was trying to increase the volume on the screen it will still show that it is low (so basically it doesn't look like it my speakers that have a problem but my head unit)
While I doubt that the fact that the mechanic worked on the abs has anything to do with it, I thought I shall mention just because before that it was working fine