I did an extensive search for this question and I saw that some people had it resolved but I tried most of the suggestions and didn't have any luck. Last night i was using my macbook on the internet with no problems, went to bed and when I woke up in the morning I tried to check my email and the exclamation point showed up in the top bar. Someone else has a macbook pro in our house and they can get online with no problem, but for whatever reason I've been booted off and can't get back on. I read some comments that said sometimes another computer can "steal" the IP address of your computer and maybe that's what happened to me? When I go into my network preferences it says Status: On but it has a self-assigned IP address 169.254.18.44 and will not be able to connect to the internet. I've tried rebooting the system, rebooting my computer, deleting the wifi passwords off my keychain access, removing the network names and readding them.... nothing seems to work. So... please help? Thanks!