My screen is starting up to black. If I sometimes get a picture it then goes black at some point. I made an appointment with you for tomorrow morning.
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The issue of your screen going black doesn’t sound like it’s going to be resolved via anything that we could do software wise. This is very likely hardware related. While we could try a few things as precautions I feel strongly that none of those software guesses would resolve the issue.

Ways to troubleshoot:

Connect the computer to a second monitor.

If only the computer monitor goes out but the external monitor stays on and works properly, then software is ruled out. If both monitors go out then it’s most likely the graphics card on the Mac itself.

The next time it goes out, you can also shine a flashlight through the Apple behind the light (if it’s a laptop). If you can still see desktop images then it’s most likely the backlight and therefore also a hardware issue.

We can keep the scheduled appointment but I fear you may only be paying me to tell you the bad news that this would be a repair done by Apple.

In short, most likely either:

Failing backlight
Failing graphics card