I run into problems with using 2 time capsules in my network.

The 2TB Time Capsule I bought some weeks ago is used as the main router/switch (connected to my provider's modem). To this TC I have connected an Airport Express to cover my whole house.

I want to use my old TC (1TB) previous generation to extend the network (by wire to the main TC) in order to connect my Marantz SR 6006 Receiver and also my windows PC in the same room.

The Main TC + Airport express were working perfectly until I added the "old" TC into the network. Now I lose network connection completely and when I use airport configuration from my IMac it states that it doesn't find any airport device.

How can I effectively use both time capsules without losing my internet connection.