MacBook Air and Apple TV: Excellent Connection to Time Capsule...But No Internet!

I've recently set up a new network at my house. I live in a building with wireless internet but no ethernet jacks in the walls. I was able to set up an AirPort Express to wirelessly connect to the building wifi and serve as a bridge between the building Wi-Fi and my Time Capsule. I've used the Time Capsule to set up a private network, which I use to connect all my devices. things seem to be working smoothly, but now my MacBook Air has no internet. It connects to the private network I created (via the Time Capsule) with no problems, but indicates there is no internet connection. The laptop was able to connect before and I have not changed any settings. Currently, there are no problems with my iPad and iPhone connecting and getting internet through the Time Capsule private network (and yes, cell data service has been turned off on these devices - as is the building wifi - so the internet is definitely coming thorough the Time Capsule network). I also have the same issue with my Apple TV (excellent connection to network, but no internet), so I don't think this is a device-specific problem. I'm not sure where to start and would appreciate help!