HOW you set up the network we can't tell you what your problem is.
It is LIKELY that if you set up wireless security you chose a security protocol that your Nook does not support. Since you mention that you were not "asked to create a password" it is more likely that you did not set up any security on the router but your Nook still thinks (because of how it was initially connected) that it is trying to connect to a secure network.
What you NEED to do is get out your router's manual and follow the steps to set up the network and wireless security.
AFTER doing that you set up each node's connection according to the instructions provided with the device.
After a recent storm, my wireless network disappeared. I created a new network and was able to get my desk top, lap top and printer to recognize the new network. However, my Nook Color keeps asking for a password to access the network. When I set up the new network, I was not asked to create a password, and the password for my old network does not work. How do I link my Nook to my wireless network?