Internal speakers work, but audio jack doesn't

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http://askubuntu.com – I have a 12.04 setup in which Audio works well from my laptop's internal speakers, but as soon as I plug in my speakers or headphones, the 'Mute' hardware light on my laptop lights up and obviously there's no sound output. Any ideas on how to fix this? HP DV6 6121tx Ubuntu 12.04 (HowTos)