Turns on and off three times - ME too!
I have done a bunch of xboxes with very few problems, but I had never done a 2.6 chip in a 1.6 before.
At first, I had the same thing this person describes. Then, after finding a missing solder point I got the flashbios. I then used my disk with bios 4981.67. It read it and flashed it and then turns the box off. When I turn the box on, it turns on and back off three times. Just like the prior writer describes.
Does anyone have a suggestion? I am stuck.