My friend gave me his 1.6 xbox to fix, he said it showed nothing on the screen.

When starting up, it has the "coma console" symptoms more common of 1.0-1.5 boxes, except that the cd tray still opens and closes, but there is no audio/video, and no error lights (ROL is just solid green)

Assuming the ROM somehow got corrupted, I installed one of my old Xenium chips, and it boots fine to the Xenium OS (I can see a picture on the screen, and change settings, etc.), but as soon as I try to run a hacked bios like M8+ it goes back to the black screen with no audio, no error codes, nothing.

Anything? I'm just about to tell him he needs a new motherboard.

Make sure t's not a corrupt eeprom. I would try flashbios unauth. w/ embedded eeproms. If you can boot that, you can flash a generic 1.6 eeprom. Beware of HD locking issues though. (Don't know what the Xenium OS offers for eeprom backup/flashing.)

Yeah I think it was the eeprom, I changed a bunch of eeprom settings in the xenium os and it finally worked, I don't even know what I actually did, but it boots fine now.

It should be interesting to note that even though the xbox wasn't brand new (the hdd had saves and stuff on it), when it first booted to the MS dash it asked to select a language, time zone, etc, as if I completely reset the eeprom somehow.