You need to enable PulseAudio through PCC - Hardware - Sound and then immediately reboot.Thanks Just18. Did that first up. Still no good.
Anyway after thinking about it some more it suddenly came to me. I use the headphones 99.99% of the time. Plug them in the 'line in' at the back. Problem 99.99% "fixed".
That will do for now. Time to check out pclinuxos.
Line in? Don't you mean Line Out?
Line In is an input for a sound source (e.g. tape deck or turntable). What's the other 0.01% you implied in "99.99%"?
Um... you don't have your sound card set up for 5.1 channels out, do you? If so, the Line In may become an output... and this may explain some of what's happening, too.
Is all the trouble you've been having while you plug your headphones into the jack on a set of speakers? Here's a suggestion, but be sure to turn down the volume first and gradually crank it up - otherwise you could damage your ears and the 'phones:
Try different speakers or bypass your speakers by plugging your 'phones into the speaker output directly - this may be a relatively simple but intermittent hardware problem. (The headphone jack on your speakers may be defective...) I'm not certain of this, by any means, as your symptom set seems very strange, indeed, but check it anyway just to eliminate it. Please note the cautions above - high volumes can really hurt your ears when applied very suddenly.
Something I do with my laptop is use a stereo Y-connector so that I can plug headphones in without disconnecting speakers (My speakers don't have a headphone jack). A few bucks at Wal-Mart or Radio Shack puts one of these in your hands.
Hope this helps you find your solution.