I have a MacBook Pro 15" which I got about two years ago. I'm using OS Lion 10.7. I didn't had any problems for two years but about a month ago our wifi had a little damage. So we bought another one, the same model. First none of the devices were connected but then our iPads and iPhones did. Then my sisters macbook pro which is the same of mine, got connected. But everytime I try to connect it says "Alert: no internet connection". My Macbook can find the wifi, but it cant connect it. When I open network preferences, It says "Wifi does not have an IP address and cannot connect to the Internet." But my sisters macbook with all same settings with mine can find the IP address! I really need help, Im a student and my homeworks are on websites so I should connect to internet. Hoping for answers .
P.S ( English is not my native language, so sorry for mistakes )