Group Seeting Or Security Issues

[IcedDante]

The basic gist of it was that I was having user Groups problems, was unable to see several menu buttons like the Synaptic Package Manager, and I fixed this by running:
usermod -a -G admin userNameHere

This solved some of my access problems. I was, however, having a problem with no sound that I reported here:

http://ubuntuforums.org/showthread.php?t=792090 and was advised to add myself to the Sound group under the User Privileges tab of the Users and Group editor.

When I went to this tab- I found it empty for both myself and root. I don't know why this was, but I clicked on OK to leave this window, and I think that by doing so I inadvertently wiped out the groups that were there originally. After rebooting I get a bunch of ugly terminal output and no Ubuntu login window.

I tried repeating the usermod command and I now get the message:

The GDM group "gdm" does not exist. Please correct GDM configuration and restart GDM.

And I am redirected to the shell. Where should I go from here? If I type in groups for myself, I see only: root.

Thanks!

One question that I think might help get me started- is there a way to:

1. See all available groups
2. See which groups I belong to
3. Add myself to these groups

via the command line?

I ran: cat /etc/group

and got only this for the output:

root :x :0 :
nogroup :x:65534 :

Please help, my friends: my machine is unusable!

I was on the Ubuntu IRC channel and was informed that these problems might have been started by using sudo to run GUI applications (instead of gksudo) which was a valuable lesson learned. The one who told me about that did not have any information on how to fix my current problem. I am hoping someone here does.

I know these forums are a volunteer effort, but I have still received no reply (is my problem that dire or obtuse?) so I demand nothing but I ask that if you can provide any help or at least point me in the right direction that you do so.

Many thanks to y'all!