well...I'm probably showing my own ignorance, but what kind of server are we talking about? Windows Server 2003? 2000? Linux? Novell (heaven forbid..
? Apache? (see also Linux..
How is your account set up? are you the actual admin of the server? or just have rights or permissions? how is the security set up? (Don't answer that here, but just think about it)
has someone changed your password? have you checked the case of your password (upper, lower)? Passwords (on the servers I use, at least) are case sensitive. Maybe it's expired, or doesn't meet security guidelines, etc.
Just give us a little to go on, and maybe we can figure it out.