Welcome to the forum.
There could be multiple options why you experience this problem.
First off all the problem could be with hardware or software.
A little bit of the hardware can you examine your self. Are there any visible damages on the screen, except some light scratches. If so you have to go to a professional repair service. Or was the phone really hot when it happened? Because the phone protects itself for being overheated by minimizing every single process and reducing the brightness to the very minimum. Then you just have to wait until it cools down. Turning it off and keeping it out of the sun would be great.
If it is a software problem it's probably a virus.
Do you still have the AVG anti virus app on you phone? Because I know from computers that there are viruses that can make you screen go black, maybe you got a virus on you device somehow.
If you have the app you could take the following steps:
1. Check in the play store if you have the newest version.
2. Open AVG protection.
3. Open the menu by tapping in the upper left corner.
4. choose settings anti virus.
5. Choose security settings.
6. Set the sensitivity to the maximum.
7. Make sure the external storage scan is checked on.
8. Start a scan.
9. Wait a few minutes.
10. If necessary let the app clean up you device.
If that didn't work you can try to scan for malware. I use malwarebytes because it's simple, it's free and has an active protection function.
To scan with malwarebytes follow these steps:
1. Download and install malwarebytes using the play store.
2. Tap on scan know.
3. Wait while the scan is going.
4. If necessary let the app clean op you device.
I hope this helps.
