Chosen Solution
My problem is due to a 27-inch iMac Late 2012 Quad Core Processor 2.9, was replacing the HDD of this machine, the Mac I then lit the job done. Shut down your Mac and try to light again but this no longer wanted to turn more. I have tried to make it on again, and change the power supply, replace the battery of Mother Board, Remove all electronic parts and place in anti-static bags but the iMac does not react. When connecting your iMac to the electric current, is not none of the LEDs lights of diagnotico.
Check the wall plug. You should at least get #1 diagnostic light on if it is getting power.
