I connect to the Internet with my Time Capsule's Wi-Fi, and it works perfectly. I also have been backing up to the same Time Capsule with Time Machine. But now, after about 18 months, Time Machine complains that it can not find the backup drive. I checked AirPort Utility, and there I just see the "Internet" sphere and the green dot letting me know I'm connected successfully. The Time Capsule neither shows up nor can it be discovered.
I rebooted the Time Capsule several times. LED is first yellow and then green, like I'd expect as normal.
What could be wrong? How can I troubleshoot?