The screen does not light up at all, even though the phone is actually

The screen does not light up at all, even though the phone is actually "ON" and is responding. First time when I noticed that the screen is not lighting up I thought something is wrong. Then all of a sudden the screen lighted up. This kept on going for a few days. The screen keep lighting up on and off. Now since last two weeks the screen has not come up at all. Strangely, the phone is working. Because we can experience the phone vibration whenever there is a call or a text message or any other notifications (like WhatsApp messages, Facebook posts notification etc). The moment phone is in a home Wifi network and gets connected to internet, it starts beeping with notifications. In fact, if I call on my number from another number the phone rings, vibrates. Only the problem is with the screen. The screen does not light up. For sure, the screen was responding perfectly the last time when I saw that screen lighting up. Is there a known solution to this problem ? Eventually, if it doesn't work then I will have to visit the service center. But meanwhile, is there a way to diagnose or a way to find out what is wrong ? Any known method that can be followed as trial before visiting the service center ?