Windows cannot connect to domain controller

Hello i have a problem and was wondering if anyone could help me out as i am fairly new to this game.

I have an error “Windows cannot connect to the Domain Controller, either the Domain Controller is down or because the computer account was not found.”

I am using XP on the machines and server are 2003 server, we use active directory and have Exchange and Domain servers.
I have tried changing network cables and that doesn’t solve anything, I can ping the network but the network but the network cannot ping me.
I am logged on the local administrator, but when I log on as network user it gives me the error?

Any ideas as I am lost at the moment?