press ctrl+alt+del in welcome screen
in the popped logon window, type administrator as user name
and password is the one u set on installation, or blank password if u have never touched it
once u r logged in, then u can go figure out what's wrong with ur profile
if u cant find any problems, just wanna fix the logon problem, try to replace ur profile with administrator's one, or default users' profile (using copy & paste)
default profile path: c:\documents and settings\