TC keeps disconnecting from my Win7 PC

Hello.

I have a MacBook Pro, a Desktop PC running Windows 7 and a wifi router connected to the Broadband Internet.

All devices share the same local network.

I recently bought a Time Capsule for using as an external wifi HD, to share data between all computers, but I had some problems setting everything up.

I tried the following setups at my home network, which partially worked:

Setup 1

Internet Modem <--[ethernet]--> Router

Desktop PC <--[ethernet]--> Router <--[wifi]--> MacBook Pro

Time Capsule <--[ethernet]--> Router

Setup 2

Internet Modem <--[ethernet]--> Time Capsule

Desktop PC <--[ethernet]--> Time Capsule <--[wifi]--> MacBook Pro

The problem happens when copying data from my Windows PC: eventually, the connection between it and the Time Capsule is lost, interrupting the copy. It keeps happening every time, after a while, and only gets fixed rebooting Windows and the Time Capsule. I couldn't copy my whole PC data, since it has around 150GB of data...

Why it happens?

Can someone help me setting everything up in a "stable" way?

Thanks in advance.