This computer has been having intermittent internet (adsl) dropouts… but always behaves itself when I’m there… The internet did drop out after a few visits & the behaviour was quite strange… sometimes the response to pings was extremely slow, sometimes the connection was just fine, other times the internet was off-air for a few minutes straight.
I eventually realised that someone (before me) had placed a network card into the PC (but the PC had a network card built-in to the motherboard).
There is no indication as to why this was done. So I guess that the built-in network port had developed a fault… I wasn’t going to waste time testing the “faulty” network port… so I just disabled it via windows xp, so that all network services are forced to bind with the plug-in network card.
The moral of the story is to never assume that a pc is configured in a reasonable way.