Dell latitude - headphones stop speakers to work

I recently bought a Dell latitude E6420 i5-2520M 8GB and I am experiencing a very aoying issue with the speakers.

The sound coming from the speakers worked until I plugged in the headphones jack into the computer for the first time - after that sounds comes only from the headphones and the speakers don't work anymore.

What is strange is that every time I uninstall and reinstall the sound drivers the speakers start to work again until i plug the jack of the headphones and again speakers stop to work.

What I have tried so far with no success:

• Uninstall and reinstall original audio/sound drivers
• Install Realtek sound drivers
• Recovery and reinstall Windows 10

Any Idea?

Please let me know what you need to know about my computer to better understand the problem and I will amend the question accordingly.

Thanks!