Why my sound is mute? I have problem with my mac mini, sound icon is mute and i am unable to click to unmute it.

Tomorrow night it was working fine, but getting issue now, i inserted headPhone but nothing happen.

  

and 



list of Audio devices uder System Report
From the screen shots you posted it appears that your Mac doesn't think it has any sound output devices.

This could indicate a hardware fault.  If after rebooting your Mac there are still no output devices listed in System Preferences &gt; Sound try running a system report. 

You can access this by choosing About this Mac from the Apple () Menu and then pressing the System Report... button.

On the left of the System Report window there should be a section for Audio.  If you select that you will get a list of Audio devices.  If that is empty you most probably have a hardware fault and need to take your Mac to an Apple Store for repair.