i know this isn't c++, but please just help me!!!

ok, something REALLY bad has happened to my computer. I'm not sure exactly what happened, but it's one of two things: I installed windows XP updates (some new critical update thing for networks or whatever), and also that bridge-building software

so, I had to reboot my computer when i installed the bb software, and then when i load up xp, it goes through the load process and yadda, but then when i get to the login screen, nothing comes up except the mouse and two error boxes, one of 'em's something about lsass and another is about some dll

please, i'm begging for help here (if you're wondering how i'm talking, i have a second computer that I'm on)