The first thing I did was to remove the PCI card. In one slot it would not allow the machine to power down and in the other it would stall on boot sequence. I replaced the old USB1 card which was hard-wired to the motherboard.

By the time I got internet back, it would log on from boot, then hold the connection for about 5-10 mins, then suddenly drop it, although bizarrely, I still had email. Not only that, my laptop, which used a wireless connection to my router, was functioning perfectly.

At the behest of the ISP technical support I uninstalled ZoneAlarm, disabled AVG Antivirus, removed a piece of spyware detector but all for nought. 40 minutes of telephone advice and all he could tell me was that I had a software conflict.

I disabled just about every damned thing I could find and went into the registry editor, found all the remaining ZoneAlarm entries and deleted them. Zip. Nada. Still malfunctioning.

A more knowledgeable friend called by. We tried installing Opera browser but not dice, so in the end we reloaded ZoneAlarm and, VOILA, it suddenly worked again and is working now. Just to be on the safe side I have disabled the router firewall to stop potential conflicts with ZoneAlarm.

I have absolutely no idea what the hell was wrong. All I can say is that all is now right with the world.

As was said above, case closed.