I think, you seeing the green orb for a second, is what happens on mine when i dont have the network cable plugged in.
This is what made me think the network cable slowed down the boot process, because it never gets to the green orb when connected to a network.
This, however, i think only applies to v1.4&1.5 xbox's. This is why people are having bother with older xbox's.
Anyway, suggestions, make sure the network cable youve got plugged in, is sending signals to the xbox and the green light on the back of the xbox is on.
OR
Make a loopback cable like instructed in previous posts.
Apart from that, i think you just gotta sit it out and wait for it to come out of the loop, assuming its an older version xbox.