Help Lost connectivity with PC and Server

I have a site with 11 servers 2003 domain, with 2008 member servers.
Most deskptops/laptop are running xp with a company of windows 7 pro here and there. We have one 2003 server which seems to block pcs from accessing it.
If we then add an exclusion in the dhcp for this ip address that the servers on the pc and give it a new ip address it will connect fine. I have unistall av software and windows firewall is disabled just at a complete loss with this one