Yeah. Renew desn't always work if it already has what it considers to be a valid IP.

If that fails I'll try and get manual settings

IP address needs to be unique but in the same range as the router. Something like 192.168.0.50 should be safe.
Subnet Mask will be 255.255.255.0
Default Gateway and DNS servers will be your router's IP address (192.168.0.1 presumably).

If it hasnt been already mentioned, double check that some malware hasnt added a proxy setting within your browser settings.

just a thought

Thanks everyone for your help and advice.

Got the desktop back on line, although the LAN connection to the router still seems a bit flaky.

The ipconfig /release and ipconfig /renew commands were very helpful. Got the system to auto assign appropriate IP addresses and then pinged the router – was getting patchy returns.

Tried a few cable and router port swaps to get about 75% ping returns then tried to connect to the router admin page IP. This was very patchy until I settled on one particular port / cable combination, which got me back on line.

Virus database and windows upgrades updated, but connection quite slow and still patchy. Strongly suspect that the onboard Ethernet port is either dodgy or has been affected by a Windows upgrade.