2 pointsYou need the Avatar Update. Look in your Xbox 360 Settings to your Dashboard version and download the exactly same version and install it. If you want to boot in your own/custom Animation, you need FakeAnimation and a custom Boot Animation (here some Examples).
1 pointDr.Gonzo now it is working. Thanks well after several of attempts what I've do is very simple. I followed first all your instructions. Then I reboot the xbox in to the original dash then it read the usb finally after lots of restart I accept the update then it restart. That's all. Thank you very much from the bottom of my heart. I'm sure tomorrow my son will be very happy after selling his ps4 pro. Can't do this without your help
1 pointAgain its very important that your Avatar Update and your installed Dashboard are have the same version number. Extract the Rar. If you have Dashlaunch installed, rename $Systemupdate to $$ystemupdate and move the folder to Fat32 formatted USB Stick & connect it to your Xbox 360 and starts your 360. Your Xbox 360 should recognize the Update.