Ok this may or may not be working in your case, but it did on my win xp installation..

If you are talking about password it ask in recovery console in command line, then when it asks for password and if you enter password of user A but get incorrect as answer Then simply press enter wihout typing anything, and you will get access.

I don't know reason or any explaination for this. but it surely worked on atleast three windows xp installation where admin passwords were not accepted ...

hope this helps