Wifi passes diagnostics, still no internet.

My MacBook Pro is up to date. Wifi says it's connected, network diagnostics passes with green lights every time saying that the internet is working properly. In safari, however, I still cannot get onto any web page. It times out and says server is not responding. It's weird because my ipad and iPhone navigate via wifi without any problems. Even the girl sitting behind me on her mac air is surfing the web just fine. I already tried switching the DNS numbers out for any and all I could find thru other threads but nothing seems to work.

Plugged in my phone to update it's software thru iTunes on my MacBook and it also said it couldn't find a server.

One weird thing: I called tech support and she ran me thru the network diagnostic motions, same as before, passed diag tests and said internet was working fine. She asked me to go to a website and it worked! (First time in 4 hrs trying to get this going in the library at school). Went outside for a victory smoke and now I'm back to square one. Diag tests still pass, and no internet pages work. What is going on? I got this laptop specifically to do work at school and now I have nothing!!