This appears to be a popular topic recently so appologies for only adding to it.
I have recently dual booted a Dell Inspiron 7000 series with Ubuntu 14.04. The sound initially worked but after some time, the speakers stopped working. Its worth noting that the headphone jack continued to worked fine.
After some searching, I managed to get it working again by purging and re-installing pulseadio and alsa. However, after another few days, the speakers stopped working again. This time, purging and re-installing pulseaudio and alsa did not work.
I have checked alsamixer and nothing is muted. I have installed some additional drivers as recommended in some threads but I forget which ones.
Interesting thing is, (I think) alsainfo says my master if off:
!!-------Mixer controls for card 1 [PCH]
Card hw:1 'PCH'/'HDA Intel PCH at 0xf0614000 irq 60' ... Simple mixer control 'Master',0
But alsamixer says it is not:
Sorry, I haven't got enough reputation to post images.
Does anybody have any advice?