RDP to a Server thru PDC Admin Acc with UN PW

Hey guys
I’ve got a Dell server installed 2k3 SBS + SP2 plus most updates and patches…
-Firewall is off
-services related to RDP all enabled
-static dedicated off network IP
-UN PW created as administrator
I have no idea why I can see the server from outside from XP machines, with RDP software and it asks for UN PW but after a few seconds it will say I have to contact the administrator of the server!

The server is a domain and the admin acc is PDC acc.

any suggestions?