Ok, So you have probably come to this forum section because Xell has stopped booting or get's stuck if it does boot. I can personally say that i have had this problem, and i think that I am the first person to have a solution to it!

I only have two method's, each work's about 50-89% of the time.
METHOD 1
This is a pretty simple method, as long as you know what you are doing. This method is just to simply re-flash the nand. YOU NEED YOUR CPU KEY!!! I know it's pretty stupid for you needing your CPU key if Xell is stuck, but if you have it, Great!
Find a download to XeBuild GUI, open it, then find your nand.

[img]http://imgur.com/nV9W1[/img]
Afterwards, just fill in the CPU key info and the kernal you want your Nand flashed as, then hit "generate hacked image"

Afterwards, you can FTP it to your xbox or use a USB, and flash it using Flash360

METHOD 2
This is the method i found all by myself. You just simply take out your Xbox 360's network adapter if you have one plugged in. Easy! Xell should boot normally now!
The reason for this is because the network adapter has an "Xbox Security Method" driver pre-installed in it. No idea how that really effect's it, but that's the only explanation i could think of.