Got the following from another site:

GREEN/RED Flashing:
Probably a bad chip or bad image.

SOLID GREEN/NO EJECT/No AUDIO/No VIDEO:
Probably a bad solder point. Check all your points again.

SOLID GREEN/No AUDIO/No VIDEO:
This is probably a problems with your audio settings. Try to boot your xbox with a standard a/v pack instead of a HD pack.

ORANGE/GREEN Flashing:
No AUDIO/VIDEO (A/V) pack.

Mine flashes red and green, but its not the chip, it has booted up backups but then cuts out! I think it is overheating? Is so, what do I do to fix it?

I have had the red/green flashing 3 times now on boxes that I have modded, and every time it has been down to 1 dry joint, nothing to do with the image on the chip or anything else
Hope this helps

If its flashing green/orange and giving the call M$ screen, what does that mean? I"m thinking about buying an Xbox that is doing this but don't want to if its not as easy to fix as just switching out the DVD drive or not. It has been opened to check the connections inside the Xbox but not modded.

Might also want to check the ide and power connections inside of your xbox. That is what fixed mine.