Hey I HAVE THE EXACT same problem and my XBOX is a 1.4 as well.
The only difference is the color of the LED on my Xenium chip is RED (Solid), I have checked all soildering etc and even done multimeter checks and everythign seems find. I have even tried to boot from a EVOX disk and tried to flash the bios but nothing seems to be working.
I really hope someone has an answer to this.
Here are some of the other things ihave tried that might help you guys:
1. Try booting the box by using the Eject Button
2. When the box boots try pressing the White button on your controller if that doesnt work try pressing the black bios.
3. Try booting with a Slayer or Evox disk
4. try and using the other d0 point on your box (you have two a top d0 and a bottom d0)
RECHECK your d0.
Guys i feel your pain trust me i have been going through it, for the 2 months i have had my xbox its been 1.5 months broken with this problem!
I will keep watching this thread if anyone fixes it please let me know.