You may have reduced the brightness of your screen before and forgot to increase it. For instance, if your computer had to do some processing where the screen was not required (good to save energy).
In that case, just turn the brightness up again. Check out the don't know how to make the screen brighter solutions to learn how to increase it.
Maybe your screen is black because your device is not turned on, or maybe you have accidentally turned it off.
If you are using a computer and it doesn't turn on, check out the solutions to the computer doesn't turn on issue.
Nowadays, you can reach most manufacturers or retailers directly via live chat, email, or direct call, and have your faulty device replaced.
Check their websites for more information regarding how to contact them.
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.