Wireless network working intermittently

Hello,
I had a wireless network that worked intermittently - so I thought I would wire it via Ethernet. I have Ethernet cards in both PCs, have bought an Ethernet switch (which I thought I needed), have connected with cat5 cables and the second computer does not connect. I have a wireless router if that can be of any use or am I just missing something. Many thanks for any help as really needed by novice.