Try this procedure!
1. When the password is required, press Command, Option, Ctrl and Esc.
2. Click on "Quit" if it's possible (if the application name isn't 'Finder'.)
If the application name is "Finder", click on "Quit" (or Exit?). The computer will close the Finder, then it reappears, without the password !?
If the application name isn't 'Finder' click on "Quit" (or Exit?)
3. The protection are been disabled for the moment!?
For always disable the protection :
1. Click x2 on the hard drive disk icon.
2. Chose the "System Folder" ("Dossier système" in french)
3. Look at " Open at startup" (the name isn't Startup Items?) ("Ouverture au démarrage" in french)
4. Drag and Drop the icon(s) in this folder to the Desktop (don't delete files)
5. Close all windows then restart your computer.
6. The password not appears Again !
Note: if the system not work correctly, replace the system files on the desktop to the System Folder, at "Open at startup" (Startup Items?)
Sorry, i am not very sure!