No sound on speakers, headphones ok

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http://unix.stackexchange.com – My Laptop (Dell Vostro 3300) internal speaker (yes, it's mono) is mute already for some time, and I was just patient with this problem, because the sound quality is ridiculous anyway and I always used either headphones or external speakers. But I wanted to fix this nevertheless, for those few times I need that pity internal speaker. There was no problem initially, but it appeared something like couple of months ago. It might be related to OS upgrades (Ubuntu 12.04 LTE right now), but, on the other hand, if I boot Live Mint 12, then there's no sound on speakers there neither. I thought that th (HowTos)