This information is the collected work of hard working modders from around the world. It has been compiled over the past several years and is believed to be true.
GREEN / RED Flashing:
Otherwise known as FRAG (flashing red and green). This error could come from a number of different sources. A short somewhere on the motherboard, a bad chip, a bad image, a bad TSOP flash are some examples that would cause a FRAG.
Solid GREEN / No Eject / No Audio / No Video:
Some people say "bad solder points", but that is so vague. I have been guilty of doing a ton of mods and then turning on my xbox to a FRAG or an error of some kind. It's good practice to do ONE mod at a time, check your work to be clean, free from shorts and error free before you move on to your next mod. SO, check the last mod you did and see if there is anything awry.
It could also be a heat problem , make sure your fan is connected and don't store your xbox near heat sources. You can also try to open the top of the xbox and check if it goes better.
Solid GREEN / No Audio / No Video:
This is most likely a problem with your a/v cables. Try to boot your xbox with a standard a/v cable rather than an HD pack. If you added analog audio ports to the back of your console, check your solder points on pins 2, 4, 3 and 5. If you added a fiber optic audio out port to your console, check your solder points on pins 1, 6 and 24. If you added composite video, check your solder points on pins 21 and 23.
Basically if you did ANY mod the the a/v pins, go back and recheck that you didn't bridge or short any pins that are not suppose to be bridged or shorted.
ORANGE / GREEN Flashing / No Audio / Video (standard a/v pack):
This may also bridged or shorted pins on the motherboard. Most likely on or near the audio / video pins or on or around the video encoder chip. Lifted or damaged traces may also be the culprit. Inspect all traces near the area where you were previously working. Use a magnifying glass if possible. Look for cuts, scrapes or scratches.
This may also be due to bridged or shorted pins on the mother board. Damaged traces and overheating can cause this error as well.
Solid GREEN, then RED Flashing:
Bad, corrupted or empty eeprom. If you were re-flashing your eeprom to use another xbox's hard drive, make sure that you flashed the right one. If you soldered wires to your eeprom chip to dump your eeprom, make sure that you didn't short any of the pins. If you used the LPC to dump your eeprom, make sure that pins 13 and 14 aren't bridged or shorted.
Your console overheated or your hardware failed. Check to make sure your fan is plugged in and running. If it is plugged in but not running, try a different fan. If your fan is not plugged in.... well.... plug it in. Check to make sure that your IDE cable is properly seated in all 3 sockets (motherboard, DVD drive and the hard drive). Make sure the power cable is plugged into the hard drive. Make sure that the yellow cable is seated properly into both the motherboard AND the DVD drive. It is also possible that one or all of your ram chips failed. If you upgraded to 128mb ram, make sure that you did not bridge or short any pins. Your video encoder may have went bad. Honestly, it could be a number of issues.
Dead, broken or empty eeprom. (self explanatory) also see "Solid GREEN, then RED Flashing" above.