Internet won't connect!

I have many other Apple devices that are all connecting to my internet except my MacBook Pro. I was watching Netflix and it turned off last week and although it says it is connected, whenever I open an application that requires Internet it will not work. I initially took it to the IT Department at my University and they said it would not connect there due to the fact my Mac runs on OS X Yosemite Version 10.10.3, and suggested I update it. However, due to the fact my Mac won't connect to anything at all, I can't actually run the software update! I have run the diagnostic program in the Wifi bar multiple times, but it 'cannot detect' a problem. Very frustrating as most of my school resources are online and I cannot access them unless it's from my iPad. Help!