Switch from a not-installed Windows partition to Mountain Lion I tried to install Windows in dual boots (version 4 I think) in my Macbook Pro 10.8. Everything was fine until Windows boot for the first time for it's installation. The operating system was not able to find Windows related drivers on the usb key I used with Bootcamp. So, my mistake was to shutdown and try again, but now Windows can't find my bootable device anymore.

The real problem is that I'm stuck on Windows' booting partition and can't go back to OS X. I tried several times Command+R or pressing T or Option during booting but everytime I face a lock icon with a password field. The password field doesn't recognize my administrator password and I never activated the root user. For testing I tried differents password that could be default one such as 'root' or 'admin' or 'sudo' but none of them actually works. If I can get passed this step, I can actually follow other tutorials.

In brief, is there a way I can switch back to OS X partition without using option key or is there a password for this locked screen?

I wish that I was enough clear to be answered by someone.
That password I think is EFI password.
To reset your EFI firmware password, hold Command and R keys while your Mac is starting to start in Recovery HD. Then, go to the Utilities menu, open Firmware Password Utility and disable the EFI firmware password.

If you don't remember the EFI password, take your computer to an Apple Store
If you don't have any Apple Store nearby, look up here, maybe you will find something good for your situation: https://www.youtube.com/results?search_query=reset+efi+password+macbook&amp;oq=reset+efi+password+macbook&amp;gs_l=youtube.3...197.5674.0.5891.22.16.0.6.6.0.353.2286.7j5j3j1.16.0.eytns%2Cpt%3D-27%2Cn%3D2%2Cui%3Dt..0.0...1ac.1.11.youtube.1_D0FcEVNL0

P.S. you can try to remove the battery for a couple of minutes, sometimes it helps: http://support.apple.com/kb/HT3964