Problem with audio of my notebook. Audio works through pc speakers and earphones at the same time

Hi all, 

thanks in advance for your advices.

I have a problem with my notebook (HP pavilion g6 2305 sl).

The problem is that when I connect my earphones the audio of my pc don't stop, hence I can hear (music, film, ...) both by earphones and speakers at the same time.

I tried to install again the latest driver audio, but nothing was changed.

I tried to use another pair of earphones, but nothing.

I have noted that if I connect the Jack at my pc, but not until the end, the audio stops from the speakers and goes through the earphones, but only if the jack is not completly inserted in the notebook.

I read a lot of forum on the web but I'm not able to find a solution for my problem.

(ps. the problem comes out suddenly, without any signal. I don't have installed any update or new software before the problem's start)