I have a problem with sound. I once pressed the mute button on my keyboard and since then I couldn't do anything to get the sound back on my headphones (obviously, including pressing mute again).
I tried to go into alsamixer and everything seems okay, except the headphone, which seems like it has no volume at all (and it says:
Item: Headphone [Off, Off]) and I also can't increase it. As for the rest (master, pcm, surround, center etc) are all okay. My sound card is a HDA Intel, Realtek ALC1200.
uname -a: Linux ... 3.2.0-53-generic-pae #81-Ubuntu SMP Thu Aug 22 21:23:47 UTC 2013 i686 i686 i386 GNU/Linux