My MB Pro has 1 user login, it's never been changed, re-created, etc. I can login to the laptop no problem, I can goto the User control panel and change the PW and it shows the single user as the admin. However I can't install software. It comes up and asks me for the password which is then rejected. Beyond reloading the OS not sure what options are. Did a permissions repair but no other luck. Makes no sense, anyone seen this? Late 2010 MB Pro.