Why did you remove your user from all groups? Doh!
Well, there's a couple things you can do. First I would reboot and select the option "Recovery Mode". If you don't have recovery mode, you'll have to boot with your Live CD and then chroot into your hard drive install.
Then from a command prompt, run visudo
and add your user on a line like
. Save the file and exit. If you're in recovery mode, type init 2
and you should be presented with the graphical login. Then login and see if you have sudo access...
Also, note that the proper way to edit the sudoers file is to do sudo visudo
as a user...