XP Pro laptop cannot access files on domain server

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http://serverfault.com – I'm managing about 20 computer for a small business, and set up their network yesterday. We have a server that fills multiple roles, including DHCP, Domain Admin, and file sharing/storage. Today all of the computers have access to the internet and the server files with the exception of one. This happens to be a laptop and not a workstation, but it's still using hard wired internet(although I've also tested with wireless). The issue we're having is that this one computer cannot log in to the domain. At bootup, he logs in to the laptop with his credentials and logs in to the domain(called Radar (HowTos)