Why my sound is mute?
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.