Chosen Solution
My iMac display goes black a lot but if you were to shine your phone light at the screen you can actually still see the stuff on the scree and changing the dim does nothing. Somedays it works and other weeks the backlight wont come on. It originally started doing this after an update about a year ago. It would sometimes start up in safe mode for a bit and then go black again. It’s never been touched internally and pretty much barely used as it happened a few months after I bought it in 2018. Not sure what exactly is going on, but feel like it’s maybe a software issue as the backlight will work sometimes. Update (01/01/2020) It will reboot when I start up holding down Option key. But, then after a couple minutes the backlight just goes completely out. It goes out no matter how I get it to power on. Then sometimes i’ll leave it on with no backlight and then hours later the backlight will go on. I’ve tried disc repair. Everything I can think of and google and the backlight won’t stay on. I got it to work about a month ago for a week straight with no issues and then it went back to having the backlight issue. Can’t find much researching this issue as it doesn’t seem like a very known issue. Maybe at this point its best to take a it to a repair shop if it can even be fixed.
If you don’t have an external USB dtrive, simply boot into Safe Mode by holding down the Shift key on startup to boot to a pure system. You can also boot to your Repair Partition by holding down the Option key on start up and selecting the repair partition. If it works, then you know you have a software issue.
Most backlight issues have been hardware related (sorry). To disprove the software side you could create an external bootable drive which has a fresh OS install and them use it to boot your system. If the problem persists then you know its a hardware issue. Sorry you waited so long to look into your problem as it might have been covered by warranty (check your sales slip and if you live in a country with two year warranty you might still have a chance).
