I've got a friend's xbox here, he said it wasn't booting so could I take a look. Well, I plugged in and it worked. As soon as you turn it on, it comes up with the SmartXX boot screen where it lets you choose your BIOS. Chose Evox and off it went.
Then I turned it off. Then back on. And I see what he means - first the generic flubber animation comes on (interesting, it doesn't do that when it works) and the MS green screen of death comes up with error code 13.
Any number of power cycles using the power button doesn't help.
But if I remove the power cable altogether and plug it back in, it'll start up straight away. Once. Then next time you shut it down and power it up again, it's back to the flubber animation followed by error 13.
It's as if the modded BIOS isn't kicking in at all and it's reverting to the original, which is looking for the original dashboard.xbe which probably doesn't exist. The modded BIOS won't work until the power cable is yanked and re-plugged.