I really don't have a clue what I have done.. each time I go to log in it says worng user and password. sometime I get an err about some kind of server. I was playing with XDMCP... could this do it.....? it is really bad I can't even log in as root!

Well, it seems unlikely that experimenting with XDMCP would cause you to lose your ablity to log on, but without more info I would not rule it out.

I have a few questions that might help people here to get a better grasp on your problem.

1) What distro and version are you having problems with?

2) When you are trying to log on, are you doing this at the console for the system, are you attempting to log on remotley, or both?

3) Can you try to give us as much of the text of any error message that you receive when your attempt to logon fails....

4) Can you think of any configuration changes made on your box recently (other than XDMCP, which you have already mentioned)?

Most distros have an option to log in from the console in a maintenance mode without needing a password, if the problem can be identified it should not be an overwhelming problem to access the system to set things right again.