A USB to Ethernet adapter for your MacBook would be a mighty useful item to have handy for situations like this when you need a wired connection from your Mac to the AirPort. The Apple Store has them, as well as other outlets.....like Best Buy, for example, that sell Apple products.
If you don't want to use a wired connection from your Mac to the AirPort router, then your only other option would be to perform a Hard Reset on the AirPort router. The downside to doing this is that you will have to set it up all over again from scratch, just like you did when it was new, and just out of the box.
If you decide to do that, with the AirPort powered on, hold in the reset button on the back of the AirPort for 7-8 seconds and release. Allow a full minute for the AriPort to restart to a slow, blinking amber light status.