Lots of things could be happening. If it's "everything" dropping your 2.4GHz net, does that happen when the network disappears? That would sound like the wireless system in your Time Capsule. It has two separate radio systems, which is how you can have the two separate frequency networks. It also has a separate network, which enables your Guest network, and allows it to be completely isolated from everything else.
If it's only the 2.4 network that fails/disappears, that's more likely to be the radio system getting flakey. A 2 year old device shouldn't really be failing, but it can't be ruled out.
I'm also going to move this thread to a more appropriate forum, since Time Capsule isn't exactly an application...