XP Log on problems (in safe mode/normal/anything)

[vyse]

Whenever I try to log on, whether in safe mode or regular, a blank error dialog with Yes or No pops up, once I click either choice, it proceeds to log in, but then automatically logs back out into the welcome screen again. It happens for safe mode too. I tried the recovery cd, but i can't get past the adminstrator password. Any tips?

Thanks in advance!