I never thought I would be that unfocused but apparently I did... I disabled the Administrator user and created a new user with password. Unfortunatly I forgot to add this user to the remote access users group. Now I cannot login anymore to this server, which is 1500 miles away, btw. Luckily (?) we have other servers in the subnet.
I tried accessing it via regedit -> connect to remote computer; but I couldn't connect to the server with the credentials of the new (and only) user.
They are all Windows 2003 R2 Servers.
Thanks in advance!!
I would attempt to make a connection to the servers admin$ share with the newly created credentials and then use compmgmt.msc to add the user to the necessary group to allow remote desktop connections.
You should then be able to connect to the server.