DHCP won't assign an IP to the server, but all other devices are fine

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http://serverfault.com – I have several devices on my network (PC's (wired), laptops (wifi), iPod (wifi), Wii (wifi)) including a web server (Just a normal PC with Ubuntu Server installed) using a wired connection. All devices are successfully assigned an IP from the DHCP server (DHCP is on the router). I used to be able to connect the server to the network. but for some reason, no matter what I do, the server is no longer being assigned an IP. Every other device works fine, and can even access the internet. the server can't even connect. MAC filtering is off, so that's not blocking the server, wired connection is use (HowTos)