I'm trying to download a new software, but then it tells me to type in the administrator's name and password, and I do, but it says "You must type an administrator's name and password to make changes to installer", so I type in my login name and password, but it doesn't work. And I'm the administrator, and this is the one and only account on this iMac. Please help me.

I'm trying to download a new software, but then it tells me to type in the administrator's name and password, and I do, but it says "You must type an administrator's name and password to make changes to installer", so I type in my login name and password, but it doesn't work. And I'm the administrator, and this is the one and only account on this iMac. Please help me.

you should have a separate administrator account and run as a basic user, if not this causes a mulitude of security problems, try using the username root and your password, otherwise your a bit stuck and may ave to back up and reinstall, it's no big deal and if you backup regularly (as you should) its relaxing. make sure you set it up correctly though with 2 accounts you as a limited user and an Admin account purely for installs.