Password works to login, change PW, but not to install software

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.

 

Everything...not a big deal, I'm on Exchange and all data is on the server so I'm about to pop the disk in and reload.