Time Capsule isn't being found by AirPort Utility

I have a MacBook Air (mid 2011) running OS 10.7.5. Last month I bought a new Time Capsule, and I would like to reformat/erase my old Time Capsule (about 5 years old) and give it to a friend. But right now, AirPort Utility cannot even find the old Time Capsule.

We wanted to test whether the old Time Capsule would work at all with my friend's ISP and Windows PC. We got them to talk to each other, but then we probably typed in something injudicious (an IP address, I think). Afterwards, we couldn't talk to the old Time Capsule with the PC, and now I can't talk to it with my MacBook either. When I use it directly as my wireless router, AirPort Utility no longer finds it - no Time Capsule icon at all, just a spinning wheel and a message saying it can't find anything but it will keep looking. (I never succeeded at locating the old Time Capsule when my new one was providing the wireless, even before we made things worse).

So the primary question is: what can I do to obtain any kind of access to my old Time Capsule - just enough to reformat it and start over? (There's no data on it that I need to care about.) Or can it be reformatted with some magic button press or paper clip insert on its own?