Richard - Polyswitches do fail, they have a maximum voltage they can protect against and within the voltage range they are protecting from they are rated to switch at least 6,000 times and protect for 1,000 hours.

If it is polyswitches you would expect only the interface they are protecting to go down. So if they are on the phone line then only the internet/ADSL should disappear with the LAN functioning as normal, ie you can get to 192.168.0.1 from your computers. The LAN side may have one set of polyswitches for all the connections or a set per connection. If it was a wireless router (don't think it is) wireless would still work and wired wouldn't.

If you have Norton Internet Security on the computers, deinstall it and microwave the CD so your not tempted to reinstall.

Be careful testing that can reach 192.168.0.1 as Internet Explorer has allsorts of way it can get itself knotted up when the network on the computer is functioning correctly.

Testing the LAN.

If you get a light on the router socket you are connecting to then you have a basic network connection and it isn't the connection hardware.

If network icon up successfully in the bottom right corner then the router/switch it is are connected at the basic network level.

Open a command window (Start -> Run, type cmd and hit OK) type in ipconfig and hit Enter. The IP address on the interface should be in the range 192.168.0.2 - 192.168.0.254. If it is then the computer has made a network connection and used DHCP to get an address.

Type ping 192.168.0.1 then hit enter and you should get responses from the router. If so then there is nothing wrong with the network connection.

Type telnet 192.168.0.1 80 then hit enter and then enter until you get a response. If you get any text back with HTTP in it then you've made a connection to the web server on the router.

If you get to this point the network is working correctly, its Internet Explorer that is making it look as though it isn't.

Simon