These may seem obvious but may help.
-Power off and reboot
-From the list of available networks, "forget" your network and let the Nook find it again.
I know this is a delayed response but I've tried both of those solutions multiple times.
I have started having this issue as well, although mine just started a few days ago. After many hours of troubleshooting and trying various things. If my Directv receiver is plugged into the network, my Nook Color gets a DHCP error. If I disconnect Directv from the network, the Nook connects immediately. My Nook has worked perfectly for almost a year not sure what has changed. Anyone else seeing this?