[SOLVED] audio symbol disappeared

my audio symbol in the task panel mystiriously disappeared. The sound is obviously ok, though.
What to do to fix it?

What distribution?
What desktop environment?

Have you restarted your DE? Or rebooted? What have you tried?

the linux distribution is "Linux mint 17"

since I am not familiar with using the terminal I tried only to use this method in order to get the symbol back on the desktop panel:

menu, system settings,sound,output,play sound through, Analog output,Built in Audio

I could not find any symbol to regulate the volume of sound.

there is additional info: not only the symbol for the regulation of the sound volume on the panel has disappeared. Nowhere can I find an icon or symbol at any other place. The volume of sound can only be changed by using the separate loudspeakers.
Which sound program should I get to be installed?

You were asked questions in post #2 that you haven't answered:

. Which desktop environment are you using?

. Have you tried rebooting?