Jim Coates -- 14th year on the Dell Laptop Audio boards -- since 2/6/04
As ridiculous as this sounds, I stubled upon a remedy from a fellow blogger. In order to fix the sound on my Dell Inspiron laptop, power it down, then PULL THE BATTERY for 10 seconds, restart the computer, problem solved... for real!
Up to that point, I literally spent two days unistalling and reinstalling software and hardware, then 4 hours on the phone with a third party support service, who insisted it was defective hardware. My persistence in seeking a solution paid off, and in this case unbelievably simple.
Headphones now work well also! Give it a try!