I just bought an iPhone 5s from someone and used it for a day and started having problems. It doesn't want to respond from touch some places and letters while typing a message. Then it got worse by not moving at all to my touch and bouncing places on it's own. Opening apps by itself. I called the guy who I bought it from and he said it's the screen that he would replacer he screen for free this week. Could it be just the screen or is it internal?