problems after migration & shortuser change

I got a new iMac this week and migrated the contents of my older Mac using Migration Assistant. About 10% into the migration the operation failed and the new computer rebooted automatically!? I started the migration over again but this time I could not use my same user and had to create a new user. Finished the migration and set everything up. I then deleted the old original user and rename my new shortuser to the old user name. After that I started having problems - couldn't authenticate on the user such as on any control panel item, but could log in at the startup screen.

I restarted into single user mode and reset the root password. Now I can at least authenticate using root - but my old user still won't work for some reason. I've tried changing the shortname back to what it was but no luck. When the system asks to authenticate it just shows a blank user field - whereas before it would show my name.

How can I fix this giant mess I've created? 🙂