Hi all,
First, sorry for my English. I am from Spain and my English is not one of my virtues. If you don´t understand anything (I wish any), ask me, no problem.
I bought an iMac 5K late 2015 (1Tb FD and R9 M390 version) on December. A few days later started the problem with the black screen. When I started it up on cold, the screen kept black (black but turns on) and you only saw the cursor in the corner. You can move it, but only it.
I had the problem with the sleep mode too. They are 2 different problems I think (perhaps with any relation), because when I returned from the sleep mode the screen kept black too, but in this case turns off.
I called Apple care, I did eeeeeeverything you have just explained (reinstall Osx, reset PRAM, SMC, etc.) Nothing of them resolved the problems. Finally I carried my iMac to the official technical service. They did every Apple hard test with no results, they changed my screen and my motherboard, but the problems persisted. They came to my house to see how it was installed at home, perhaps searching any fault, but I don´t have any strange thing and no extra and no devices incorporated. They saw everything was OK and they said me that they couldn´t do anything more for my computer.
I started a fight with the retailer to return my money and after months I got it.
With my money, I bought another this week, thinking it could be a bad product and I had bad luck. I received it on Wednesday, and today, the problem has appeared again. I am desperate with this. It cannot be bad luck, and probably it is a manufacturing defect of Apple or an OSX bug.
There is no info about this in spanish forums, no info in spanish, the only info I could find about it was in this forum, so please, have any of yours resolve this problem definitively? Is an OSX problem? I don´t know what to do, if I should keep the iMac and wait for an OSX update or return it to the Apple store. I love this iMac because its screen is amazing and I wouldn´t like to return it if the problem has any real solution.
Thank you very much!!