Remove the battery if possible, wait 30 seconds or more, then reinstall the battery and restart your phone. If you are unable to remove the battery from your phone, you must allow it to completely discharge. Then recharge it and try again to restart the phone.

Remove the stylus if you have one and see if it turns on the screen. If so, go to Settings > General management > Reset, then select Auto Restart and set a time for your phone to restart. You'll have to wait until then to see if an automatic restart resolves your issue.