My MacBook Air (about 4 years old) has started to not connect to public and private wifi which isn't ran by an apple extreme. I say this because my home and the Apple Store it works fine but at other people's houses or free wifi places it doesn't. Does anyone have any ideas? Running laterst OSX and have tried a couple things With the DNS but I'm not mega techy but am decent enough. It's hard to test though as it works at home so any changes I make I need to be somewhere else to be sure.