Whenever I make a phone call in which I have to press numbers on the keypad after dialing it turns dark. I phone. The other side answers. They instruct me to push numbers on the keypad. I push a number. The screen flashes off then back on, but doesn't register that I pressed a number. Every time I try to enter a number it does it, so I can never enter a number. Any one else have this issue? What do I do about it? Thanks.