Unplug the scanner, pull all the batteries, hold the power button for at least 30 sec and randomly press any other buttons. Repeat several times if necessary.
Try an Earphone to see if you get reduced audio? Also check weather channels to see if you get any audio from those? Also how about keypad beeps, any sound at all?
Default the scanner as listed and make a new SD card and replace it should work did it stop over night or what. is it scanning do you see it stopped on a channel.