Help with wireless LAN dropping local computers

Hello I have a small office with 2 desktop pcs running windows 7 and a couple of printers etc. They are connected through a Thompson wireless router. (connection wireless)
I was setting up a Windows 7 Homegroup which went fine and worked ok, however have now noticed that when I go to either pc within the home group it says “no other members of the homegroup are available”?
The other pc is also not visible below the network icon either. Have tried machine self diagnostics without success. Where should i start.
PS.. Internet works fine on both machines.