I might not be the one to answer your question, but I can tell you a format to post with that will help those who can, help you more readily.
First, start by telling ur Xbox ver, chip ver, and Bios ver that you want to flash.
Next, (This one is important!) CONFIRM to us the EXACT position of the switches at the time when this occurred.
Lastly, make sure you state EXACTLY what you mean by the "Backup doesn't work". How are you pressing the buttons, ie, "I press powerslightly before I press eject then hold them for 1 second, etc"
Then tell us "I get a black screen and sound, but never video, etc.
Happy Modding, hope this helps you find your answer.