Take the frame off and look at the diagnostic lights to the right of the RAM slots.
Also hook up an external monitor. This is a probable GPU failure and you may need to do a reflow on the GPU.
LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.
LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.
LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.
LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.
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James, I have a similar problem. Curious, how did you pull data off of the HD?
- de Mike Taylor
One of the easiest ways is if the system is still able to boot up is to put it into Target Disk Mode. Here you connect your broken system to another Mac to recover the files. You could even migrate all of the user settings using Migration Assistant to a new system as well!
Otherwise you can pull the drive out and using a powered SATA to USB adapter connect your old drive to a new Mac and do the same.
- de Dan
Mike. I used a lightning to lightning cable. I purchased a new mac so it was easy. In all fairness I also had apple suppprt stepping me through it. I still need to pull it out of the old computer. Gonna make a 2nd external for backup to the backup.
- de James