HelloPlease try the following below
- Remove the Case/phone cover. Just to make sure if the phone cover is not messing up with the phone sensors
- Try turning on the phone while on charge just to confirm if it is not power related issues
- Do a soft reset press and hold the power button for at least 15 seconds or until the phone turns off.
If none of the above solve the problem then I suggest you go for a hard reset and if still I had to say it does not work then flashing the phone should be the only solution that you have. Let us know if you need help on flashing your phone.