Switch from a not-installed Windows partition to Mountain Lion
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