The color of the power LED on boot can indicate specific issues.

This is letting you know the console is overheating. Clean it out, check the fan is working, and try again.

Can also mean bad BIOS/EEPROM or failed mod chip install.

This is almost always a bad BIOS/EEPROM.

This indicate the BIOS/EEPROM is bad, or has failed to load. Check the BIOS, look for trace damage, and if any mods were done perhaps reverse them first.

This indicate the BIOS/EEPROM is bad, or has failed to load. Check the BIOS, look for trace damage, and if any mods were done perhaps reverse them first.

Shorted or torn solder traces between chips. Check for solder splashes or trace damage.

Overheating, or there may be an issue near the temperature sensor chip at location U6F1.

This is the most common, and simply means there is no video cable connected. Sometimes the video out circuit or port is actually bad but its normally just the cable.

There is a potential the SMC (a PIC chip that handles low-level control and AV cable detection) is bad, but it is much more likely you just have a bad AV cable.

If you do not have a cable present, you can just ground pin 19 for example to set the cable detection into outputting NTSC Mono and bypassing the orange flashing light.

Unfortunately, this is a general system failure and can be many things.

Swap your power capacitors and super capacitor used on the clock.

If problems still persist inspect the board for trace damage, any signs of burned or bulging capacitors or blown components.

Known causes

The HDD is bad, or cables/power to it.

The DVD is bad, or cables/power to it.

Usually bad BIOS/EEPROM.