Have network, can see other PC's but no access! O.S Windows Vista Home Premium

I have for years successfully used a home LAN on a Belkin router. Now changed ISP (SKY broadband) and using their own Sagem F@ST router _ Terms & Conditions don't allow use of Belkin!!!

My PC is connected to the router by ethernet cable acting as host. A second PC is connected by ethernet cable to the router and we have a laptop linked wirelessly. The Internet can be successfully surfed and e-mail servers accessed from the host and the two networked machines. However, if I try to use the network to share files between PC's on the LAN as we have always managed to do, I get an error message telling me that the device is not found and that the name may be spelled wrong. This is true even though the devices are shown in Windows Explorer under the Network folder.

I wonder if it could be down to remnants of files relating to the Belkin (now totally disconnected). I have always managed to set up our home Network till now and I am baffled as to what can be the problem. I have jaypegs of the error screens but as a Newbie to this forum I can't see how I can upload them with this new topic.