Why is it not turning on?
I upgraded the CPU in my iMac to the i7-7700K and everything went pretty smoothly. I put it back together and tested to see if everything was working. I plugged it in and pressed the power button and the fan came on but the screen did not. I double checked that all the cables were plugged in and looked things over. When I put it back together the second time and plugged it in only the 1st diagnostic led turned on and nothing else. Now after putting the original CPU back in the first two leds are on along with the fan. The fan spins at full speed and the display is still black. What can I do to fix this?