Volume is at zero. Cannot return to normal

[AC Question]

Cannot return volume to normal.
It suddenly dropped to zero and the icon at top "Menu" bar is a circle with a line through. This same icon appears in the Setting menu

 

[Javier P]

Which phone do you have and what Android version are you running? If you press on the Volume button, can see something similar to my screenshot? If so, make sure that "all" is the highlighted option instead of "none".