The problem is that you think that you are the administrator, but you are not a full administrator, there is a hidden full power administrator Built-in Administrator Account - Enable or Disable
This was added to Vista and Windows 7 cause of how easy it was for hackers, spyware and virus makers to gain access to a PC cause the Administrator was live and active when you accessed Safe Mode. Now the Full Admin account is Disabled. So even if you do boot to Safe Mode you still will NOT see it as a account that you can log into.
You can use this full power administrator, but I do not think that you should. Using the Adminstrator is the easiest way to have less of a problem, but again not suggested. Run as Administrator