Why is my iMac display not powering?

Took my iMac to a repair place last week. He said that he isn't sure whats wrong 100% yet. They plunged in new screens replaces all the cables and other testing but could not get the lcd to power. He thinks the graphics cars is damaged partially.

After telling him what I had done and who the locking inde on the original cable wasn't working right he thinks that the computer powered on wile the cable was not fully inserted or crooked (or the data cable was damaged) and may have caused a short and damaged the card (apparently the power also follows though the cable making it easy to happen.)

He is taking the hole computer apart now to see if he can find a fix by taking a better look at the GPU (on the back side of the logic board). He has had some success repairing partial damaged GPUs in the past. I will try to keep you posted.

Keep us posted as I have the same problem. I changed the CPU. Then the iMac will not boot. Put back the original i3 CPU, still it does not go past the fans starting to blow. No chime, no light on the display. I wonder if booting up the iMac with the LVDS cable not seated could damage the GPU.

My mac repair guy concluded that the logic board was damaged. That somehow the display cable shorted out damaging the connector and nothing else. Everything else checked out as ok, including the GPU. :(

Thanks for the info. I did the EXACT same thing...it's interesting a new display didn't work, glad to rule that out...I found a logic board for $300 anyone know of one for less?

Thanks for the update. I can understand this because the LVDS cable is very difficult to insert back in the connector and I may have thought I had it in place but may have not been so it could shorten the logic board in some way. My problem is I have no external video, no startup chime, just the fans starting. Is it possible that the cable could have just damaged the logic board so that it simply will not boot at all? I have the LED lights lit no. 1 - 2 - 3. Even if I detach the video cable, the LED 3 lights. That should mean that the display is recognized. And shouldn't I even get a backlight?