Time Capsule Not Working With Time Machine

I'm trying to backup to my Time Capsule, which I haven't used in over two years. It had been displaced because of a change in internet service providers. The new provider came in with a Linksys router, setup a sub-network, and left the Time Capsule/Airport out of the mix.

So I want to return to using my Time Capsule and have since pulled out the Linksys router, and got the Airport functionality working with the existing, primary network. In other words, the Time Capsule/Airport is working to extend the range of the network.

Problem is this: I cannot backup to the Time Capsule. Even if I'm connecting to the Time Capsule via ethernet, I cannot get it past the 'preparing' phase when running Time Machine. It stays at the phase for what seems to me an inordinate amount of time (30-45 minutes). If I go into System Preferences, the Time Capsule disk doesn't make itself available when using it with Time Machine. If I choose to go into the Star Wars display of Time Machine, I can sort of see the various backups, but I can't roll back to them, and the backup indicator on the right looks sort of ghosted, like it's there but it's not there.

How do I know if the disk within the Time Capsule is failing? Could that be what's going on? How would I test it? I get a green light on the front of the TC, but not everything is hunky dory since I'm not able to backup.

Is part of my problem that I'm using a not up-to-date version of Airport Utility? –I'm using 5.4.2