You mean the proximity sensor is broken? The screen should be turned off whenever the device is close to your face. You can try clearing cache through recovery o see if that helps: power off. Hold home+volume down+power on until recovery loads. Use volume down to clear cache and power to accept. If that doesn't fix the problem then try a factory reset - be sure to backup your data first.When I'm on calls my Samsung Galaxy S5 opens several menus when my cheek touches the screen...this used to never happen, startes about a month ago, I believe my proximity sensor button is turned on, what else could it be?