My computer has been sorted, thanks to a mixture of calm, patience and a couple of long phone conversations with a friend who has the know-how to deal with these things.
It was sorted out pretty quickly in fact - within a couple of days. After that initial feeling of having lost something, however, it's felt more like the converse: I'm now reluctant, at least at the moment, to spend more than a little bit of time online each day.
Not from any sense that I should be doing other things: just that I've almost immediately found that I'm enjoying feeling less reliant on net time.
It's rather nice, in fact.