I tried t0 update my rgh jasper 512 and when i update it using xell ..the nand has bad blocks s0 i cannot access xell or nxe ...plz tell me how i acces xell.....
Unfortunately if you can't access Xell by powering the console on with the eject button you will need to re-flash the nand using hardware such as the Nand X. This will require you to open the Xbox 360 and solder the Nand X to the motherboard. You can then flash a working backup of your nand over USB, presuming you have a backup from before you updated.