As always, everything in this guide is completely at your own risk, I am not responsible for you messing up your device further nor am I responsible in the event that your Nook Color explodes and kills your cat, grandma, etc.
The Fatal Black Screen:
This is the issue where your Nook "refuses to boot up" usually after running Froyo (or possibly HC) off of your internal memory. This is usually caused by, but is not limited too, formatting your sdcard from within Froyo (or versions of HC prior to the flashable zip).
99.99% of the time, this does not mean your Nook is bricked in any way, what simply happened is your boot partition has become corrupted. For you newbies out there, the boot partition is what allows your Nook Color to turn on. The boot partition contains the instructions for what your Nook Color needs to do in order to start up and run.
Thanks to the guys that developed this neat toy, the Nook is set to boot from the sdcard before booting from the internal memory. What this means is, your nook will first search for a boot partition on the sdcard before searching for a boot partition on your Nook's internal memory. Because of this, we are able to boot and run OS software directly from the SDcard. This is how we will be fixing your "bricked" Nook Color.
First visit this link:
Download either the Rootpack, or the Clockwork Recovery image (1gb).
Next visit this link and download the 1.0.0 or 1.0.1 restore to stock files:
From this link you should also download the very last zip on the page. It is titled-flashable boot repartition zip. or something of the like. If you followed all these steps and still nothing, I would recommend flashing this as it can fix a completely screwed boot partition.
If you wish to instead restore to a pre-rooted 1.1, visit this link:
Once you have the either version of the bootable Clockwork Recovery (Rootpack or normal standard Clockwork Recovery) and a software version you would like to restore to, you must write your clockwork recovery to an sdcard to make it bootable in the Nook.
In order to do this, you must use Win32DiskImager on Windows or the command line on Mac and Linux. Follow theses instructions for writing the file to an sdcard (substitute the Clockwork file in place of Nooter):
Once the image is done writing, open up your sdcard on your computer and copy whichever restore to stock zip you choose earlier onto the card.
Now with your Nook Color unplugged from the computer, insert the sdcard and plug the Nook into the computer. Your screen should flash to life. After a short loading screen you will see a menu, using the volume keys, you are able to navigate up and down. Navigate down to the menu item that reads "mounts and storage." Navigate down and press "Format Data" then "Yes." Next do the same thing except format system. Using the power button to go back to a previous menu, return to the "mounts and storage" menu, make sure the sdcard is mounted. (If your sdcard is mounted, you will see the option to 'unmount /sdcard'. If it is not mounted you will see 'mount /sdcard'. In this case you would want to press the 'mount /sdcard' option in order to mount it. Again using the power button as the back button, navigate back to the main menu. You will see a menu item that reads "Install zip from sdcard." Select it. Now select 'choose zip from sdcard.' Now pick the zip you placed on the sdcard earlier. Scroll down to the 'Yes' option and select it. Clockwork Recovery will begin flashing the stock image to your internal memory. After a few minutes, the process should complete and you will see a message that says 'Done. Installation Complete.' From here you should remove your sdcard and navigate back to the main menu. Select the 'Reboot Now' option.
Note: Sometimes after you see the 'Done. Installation Complete.' message, Clockwork will freeze up and you will be unable to navigate back to the main menu in order to reboot. If this is the case do a hard reboot (hold the power button for 15 or so seconds so the screen turns off, then hold the power button again till it turns on).
Congratulations, you've unbricked your bricked Nook Color
TO EVERYONE STILL HAVING PROBLEMS AFTER THIS, YOU MAY/SHOULD FLASH SAMUELHALFF'S REPARTITION ZIP MENTIONED EARLIER. (LOOK UP A FEW LINES, SAME LINK AS THE 1.0.0 AND 1.0.1 RESTORE TO STOCK ZIPS)
IF YOUR STILL HAVING PROBLEMS, USE THIS LINK TO INSTALL 188.8.131.52 ON INTERNAL EMMC AND THEN BOOT TO IT.
note: to do this, you need to be able to atleast boot to the N screen.
This link has an updated bootable CWM version on it with ext4 support. Write this to your sdcard, format /system and /data and flash CM7.
If anyone has anything to add to this tutorial, post here or IM me and I will edit the OP.