if you've goofed around and tried to change your user name though the advanced settings in your mac, you may have ended up with your user switching back to a standard account. if you only started with one account, then you've left yourself with no admin account. Aaaand you can't change anything. Here's is what you do:
We're some guys and gals in San Francisco who fix macs. We can remote in and help you with stuff. It's like our job or whatever.
(five one zero) 761-6559
We charge $20 for 15 minute for quick fixes.