ok, i'm speculating here:
i just spoke with tech support and got a good idea of what's going on.
if your box was sent in for repairs or is a refurb, it probably will not work. because the xbox is looking for modded consoles, if all the s/n's on the parts inside do not match up, it will not work.
i'm more curious as to what they're gonna do if it turns out my xbox's numbers don't match up. are they going to comp me an xbox because they couldn't get the parts to match up? or am i up sh*t creek because their product stopped working within 90 days of purchase and there was no way of me knowing that this would have happened until now.
-- Taken from the xbox beta forum