Today, my wife cannot access the internet on her desktop computer running XP home. (1)The ethernet card was 'hidden' in device manager. (2)Checking 'status' shows the card enabled - but there is no device showing in 'network connections'. (3)The device driver cannot be changed, updated or rolled back if I unhide it in Device Manager. (4)System restore fails to complete successfully, leaving everything as was - although I've tried several restore points. (5) I cannot 'disable' the connection, PC says it is in use and not available to disable. I suspect malware of some form and have pulled the connection to the router for now. The PC is protected by Kaspersky Internet Suite 2012, and we've never had a problem before. Any guidance useful.
Thanks for your input guys. No sign of malware, virus or other malicious code - so invested in a 10/100/1000 ethernet card, at a very reasonable £7.76, with free p&p from Amazon. Installed very easily and 'Hello World'. I was then able to uninstall the onboard ethernet port. The missus is pleased to be online again, so this case has a happy ending - and my mysterious earache problem has thankfully cleared up.