Thanks for the question. I understand you are experiencing issues with your Time Capsule not displayed in AirPort Utility. The following resource provides information for this issue in relation to AirPort base stations, and may help to resolve your issue:
Steps for OS X Lion or Mountain Lion
This can happen if IPv6 has been disabled. To enable IPv6 for your network interface:
1. Choose Apple menu () > System Preferences, and then click Network.
2. If a lock icon appears in the lower-left corner, click it and enter your admin name and password to unlock the pane.
3. Click your network service (Wi-Fi or Ethernet) in the list, and then click Advanced.
4. Click the TCP/IP tab.
5. Choose Link-local only from the Configure IPv6 pop-up menu.
6. Click OK.
7. Click Apply.
The AirPort device should now appear in AirPort Utility.
Hi, not sure if anyone eles is seeing this problem or it has been resolved. I just had the same issue couldn't work it out. I recently installed a virus protector onto the mac and in the protector preferences the network I connect to for the Time Capsule was seleced as a public network and hence firewalled. Turned this to private or home network and all back to normal.