First Make sure it states lsass click here and not isass click here
It is probably the former as you can't boot. Your pc has not just invented and admin password. Everytime XP is installed it requests an administator password. You would have had to choose and enter one when the pc was first setup. The file that is complaining authenticates user logons. You have probably upset things when you pressed return instead of entering the correct admin password. What was changed at that point may well have expired and the system cannot therefore log you on. Did you create a password reset floppy. If not I think you have no option but to reformat and reinstall, unless someone else know different. I hope they do.