Hello everybody. I hope I can find some helpful feedback here. Likewise, that maybe the thread can help others too. Situation: I've developed a problem from one day to the next. My iMac will by all accounts turn itself off upon falling to sleep/putting disks to sleep. The computer is silent. The screen black. The mouse and keyboard are unresponsive. There is no response to pushing the power button. I've tried a number of things, that I will details below but the only solution appears seems to be to constantly having to reset the PMU (remove power cable at both ends, wait, reconnect and power up). The iMac has performed outstandingly up until this point. Troubleshooting attempts: I've tried various things I found to similar problems I read about online. Resetting the Pram/NVRAM, removing any external devices. Unchecking 'Put hard disks to sleep when possible' in energy saver. But none of these have helped. I noticed in system report that AutoPowerOff Enabled is on. I of course can't say if that was on before, or if it should be on? Running a diagnostic test reported: No issues found. I have to point out that upon clicking 'restart' after finishing this test, the iMac just switched itself off instead. Product details: iMac: 27inch. Made late 2013. Processor: 3.4Ghz i5 Intel Core i5 Memory: 16 GB 1600 MHz DDR3 Startup disk: Macintosh HD Graphics: NVIDIA GeForce GTX 775M 2048 MB Operating System: macOS, version: 10.12.6 Storage capacity: 3.12TB Fusion Drive I would be very grateful to hear if there are any other reports like this. And of course if someone knows of a solution. The computer isn't really that old and has been kept in very good condition. I would hope that this is not a sign of a hardware problem? If it is, is there a way I can find out before having to take it to a store? Many thanks in advance to you all.