yesterday I installed 16.04 over Windows Vista. It worked perfect, until later I noticed the sound wouldn't unmute. It has a check-mark next to Mute, but it won't let me unmute it. When I go into sound settings, it lets me uncheck the mute button, but still has a little speaker with an x at the top and I can't hear anything.
EDIT: This is my output of
sudo lshw |grep -A9 Audio
description: Audio device product: 82801I (ICH9 Family) HD Audio Controller vendor: Intel Corporation physical id: 1b bus info: pci@0000:00:1b.0 version: 02 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list configuration: driver=snd_hda_intel latency=0 resources: irq:28 memory:fdff4000-fdff7fff