Problems with Airport Express

I have an Airport Express set up in my dorm room acting as a Wireless Access Point. In order for this to work, my University requires us to have it placed in bridge mode. Since yesterday, my Macbook has been having problems getting onto the internet. I can connect to my network, but once I try connecting to the Internet it doesn't work. My roommate has a HP running Vista and he has no issues so It doesn't seem to be a problem with the Airport Express itself.

Any suggestions?

It may be a security issue. As a test, try turning off security if any, that you're using. (WEP, WPA, etc.) You could also try running an ethernet cable (CAT-5) from the Airport Express to your Mac to see if you can connect that way.

Regards.