Turn off wifi on your phone - then unplug your wifi router for about 15 seconds then plug it back in - while the router is powering back up go to your phone settings, go to general, then reset - tap on reset network settings. Your phone will then turn itself off and then back on. After you're router is back up go back to your home screen on your phone, tap on settings and turn wifi back on. Find your network name, tap on it and reenter your wifi password. There you should be good to go.