Closed: Inner/Outer screens cycle on/off but if open all dark?

Recently phone needed frequent recharge. One night saw screen on, then off every 5 seconds. Checked and found inner screen also cycling. If I open the phone, all goes dark and doesn't cycle, but phone does respond and works if keys touched. Hasn't happened before. Phone has not been in water or dropped. Bought new battery but problem the same. Any thoughts on problem or repair?