All credit to TTG_Mitchell

Xell is used to grab your CPU Key for your console. Which is a good thing to have in case you need to open your KV. Install Xell is easy and takes little to now time.

Download the image for your motherboard revision. Extract and place it in the nandpro folder. Make it easy on yourself and rename the Xell file to Xell

With your LPT cable and everything still set up. You will be using nandpro again. So here we go again.

1. Click start
2. Click run
3. Type CMD
4. Type the command.

Code:
C:Nandpro20bnandpro.exe lpt: -w16 Xell.bin


Don't worry about the file size. It is meant to only write to the beginning of your NAND flash.
5. Click enter and it should starting writing.
6. Once it is done writing. Unplug the lpt cable from the PC and turn on the 360. It should boot into a blue screen. If it does then you did it right.

Getting the CPU key.

Have a camera ready to take a picture of the Fuse Set's that pop up briefly.
Take a picture that includes fuse set 3,4,5,and 6. These contain your CPU key.

Take either 3 and 5 or 4 and 6. This will make up your cpu key. 3=4 5=6 So for example. I will take 3 and 5.
3= E42D681ED06A6D1C
5= 1FFD8E48C56A2058

So my CPU Key is - E42D681ED06A6D1C1FFD8E48C56A2058

Adding either one of the two will make your CPU key.

After getting your cpu key you can write your original nand image back to the board. Or go straight forward and install XBReboot or freeBOOT.

To flash your nand image back on, use this command
Code:
C:NandPro20bnandpro.exe lpt: -w16 (name of your nand backup)