Answer by Waldir Leoncio for Sound Input device (microphone) not working

The following might work for you:

1. Run gksudo gedit /etc/modprobe.d/alsa-base.conf on terminal (if you have no access to a graphical interface in the moment, use sudo nano instead of gksudo gedit.
2. Add options snd-hda-intel position_fix=1 or position_fix=2 to the end of the file.
3. Reboot

Sources: http://ubuntuforums.org/showthread.php?t=1893142 and https://wiki.ubuntu.com/Audio/PositionReporting