*** Updated on 11/24/2007 by Wrobinson ***
Domain users are not allowed to log on interactively to a server by default. In order to do so, a user or group must be granted the “allow log on locally” right (see http://technet2.microsoft.com/windowsserver/en/library/15744f9c-e188-4fac-ac60-9380a58b30ae1033.mspx?mfr=true).
This can be done using Active Directory group policy if it is needed to apply across a range of computers. It can also be applied locally, so long as no domain group policies override it. If the server in question is a domain controller then the change must be made to the default domain controller policy.
*** End Update ***
You mentioned that you’re not an IT person – does your organization have any IT people anywhere? Or is this a smaller outfit without an IT person?
Generally, if your organization is small, you should have an IT person – usually an independent contractor, who has been brought in when things are NOT in emergency mode.
On to your problem though…
Have you tried booting into “Safe Mode” ? When the windows logo FIRST appears, start pressing the F8 key, until you get a menu which includes safe mode.
I realize that you said you’re a layman, but since you mentioned XP and server in the same paragraph, I’m assuming you meant “Windows Login Screen”, since XP is not a server OS.
Do you have a (windows) domain?
Is your server a “real server” ? or just another workstation acting in the role?
If you still cannot log in from there, write back.
I’ll also send you some info by private message.