IMHO the problem is obviously hardware (happens both in linux and windows for example).
Therfore, I bought this:
http://www.pchub.com/uph/laptop/662-86243-8298/Singatron-Length18mm-Jack-Audio-3.5mm.html, and changed the jack; unfortunately, it didn't solve the problem. I can still hear as I used to so it seems my soldering is not very likely to be the problem.
It could be some other problem with the whole little board; it's more expensive, but can be found; for example here:
http://www.ebay.com/itm/Asus-69N0E0B10D01-01-USB-audio-jack-board-G60VX-G60V-G50V-G51V-G51VX-G60J-G5....
So this post is out of frustration and a heads up for those of you like who might think that changing the jack will solve the problem. Of course, it is possible the new jack was broken, that my soldering was bad in one of the many connectors, etc. It could also be that I get the same symptom but the problem is different in my computer than in others. Just my 5 cents...
If anyone finds a solution, please post. If the moderators know of any way in which tech support learned to solve the problem, please let us know.