Hi,
If the screen has not been damaged or suffered water ingress, then the best thing to do is initiate a ***reset*** to see if it corrects the problem.
***Not a factory restore***(data wiped).
***A hard reset*** (no data loss).
If you’re unsure how to do this then search the web for “hard reset no data loss” for your device, it will show you the key/button combinations to use.
This situation does occur occasionally with phones and is often fixed by reset procedure.
Another option would be to wipe the cache (look up how to do this), it will also prove if your screen is working if you see the options that come up for this procedure.
However if this does not resolve the issue then you may need to consider the screen may need replacement.
Other than that another option is to make sure you have a backup and try a ***factory restore (all data lost)***.
Hope this helps