XPS 13 9350 - password not recognized

I just purchased a Dell XPS 13 9350 Developer Edition with Ubuntu 14.04.

After setting my username and password during the initial system setup, I try to log in but the password is not recognized. I can only log in to the Guest Session. I'm sure that the password I use is the right one, even though there could be some issues related to the French keyboard configuration.

What should I do? This is quite annoying... Having a new laptop but not being able to log in at all from day 1.

Thank you