Internet Connection Confusion

Hello all. I will try to make this brief and provide specifics.

I am having major problems connecting to the wireless internet in my building. Some days, I am able to connect, other days, not. My roomates are having no problem connecting. It is a password protected network, for which I have the password. I have been able to connect in the past.

What usually happens is, after not connecting, I am directed towards Network Diagnostics. I select AirPort, select the network I am supposed to be using, and so on until I get the last screen- "Network Diagnostics is unable to help you with this problem, etc..." As I'm working through this, Safari tries to load websites, but to no avail.

I have all "green lights" when going through Network Diagnostics, except for "Internet" and "Server", which are both red lights.

I've checked, and my firewall is off. It also appears that I am being assigned an ISP address.

I'm at Starbucks now, on their WiFi, so I dont believe its a problem with my computer.

I think this is all the relevent info I have- I'm a newbie, so if you have questions, make em easy on me.

Any help/advice would be appreciated. Please ask if you need more info.
Thank you.