Chosen Solution
Experiencing a very strange problem with my iMac. When I shut down or restart my iMac, I can’t turn it back on immediately. To start/turn on again, I’ll have to unplug the power cable from the wall then wait for 30-60 seconds before connecting the power cable back into the (wall) power then it will turn on. Sometimes it powers off suddenly while the computer is in use. Have no idea what the problem is but looks like it needs some kind of power “reset”. But that doesn’t explain why it shuts off suddenly sometimes. Spoke to Apple on the phone and they asked me to try the following commands which I did but the issue still exists. Option 1: Shift+Ctrl+Option+Power for 10 secondsOption 2: CMD+Option+P+R until the second startup noise Hope it’s nothing serious as in something to do with main circuit or motherboard. Please suggest any solution if you have come across this issue before.
At this point I think you need to do some deeper diagnostics, The first is to see if the onboard diagnostics gives us a clue. Restart your system while pressing the D key. Tell us if you get an error message and what it was. Sadly, the onboard diagnostics has lost its shine in the newer systems. It might not give anything or anything useful. I would look at the systems cooling as a likely issue. This could be dust buildup or the systems cooling fan has failed. In both cases the system will go into a shut down condition like you’ve described. Again, lets use some software to help identify what’s happening with the systems thermals. Install this great app: TG Pro it will allow you to see the sensors and the fan values. Run your system until you get to the shutdown point and then restart your system. Now make sure all of the sensors are showing in the main window with the bars (you may need to resize it) take a snapshot of the window and post it here for us to see Adding images to an existing question.
