Did you make the carding using winimage yet? For me, that was the method that worked the most consistently.
To check it, pop the card in your reader and see if there is a single ~40mb partition named nooter. That pretty much says the card is what it is supposed to be.
Unplug the nook, power it off by holding the power button until it turns off. put the card into the nook, plug it into your computer. In a little time, you should notice it saying about a new device connected, or some complaining about not being able to find the drivers. Let it go for about a minute after that and then remove the card and reboot the nook.
If it still boots normally with the card your just made, try using another card and see if that works. Also, if you have access to a mac, before you make the card with winimage (on the windows machine), use Disk utility to partition the card with 1 partition, free space.
It sounds kinda quirky, but it is how I got it to work.