Hiya Mate, I have just installed an XBIT in my mates v11 XBOX, and we had the same problem, and i knew what i was doing because i have installed an XBIT in my v10 XBOX.
If you are certain that the XBIT is in a solid position, and the pogo pin is definetly in contact with the d0 point, and you are certain that the flashing procedure on the XBIT went fine and all you are getting is the MS Bootup then, all that is happening is that the XBIT isnt hijacking the bios.
This is the problem of the d0 point, and what you will find you will have to do is get hold of a pin, and gently scrape around the rim of the d0 point to remove some of the plastic coating that is stopping the d0 pogo, from making contact with the metal.
I stress, that you have to be very careful, this is pointed out in other threads, it took me a couple of times, as i didnt want to be to rough at first, but eventually the coloured bios i had flashed to the XBIT took over, and now i have one extatic mate who cant stop tinkering with his XBOX.
Good Luck.
Yours
Spice Guy