I tried to change the logon background but now I can't get beyond it at startup. The new background is visible but there are no buttons or anything else on the screen. Launching in safe mode doesn't help either. How can I get past the logon screen?
One time, I disabled an old username from Windows ME from showing on the logon screen, but the one I'd wanted to keep was dependant on it or something (the first wasn't even showing; I don't know why I disabled it). I logged into Administrator via safe mode, went back into TweakUI, and re-enabled it.
Maybe that's what you did? I too sometimes get caught up in many tweaks and blame one mishap on the wrong program.
I had this problem before when I was designing my own logon screen. Something went wrong and the buttons didn't work and I couldn't login. To get around the logon screen hold down CONTROL and ALT and press DEL twice, this will bring up the classic style logon box.