Thanks both - it was Mr mtc who posted, and after spending a merry half hour on the phone to Swisscom it's all sorted. I don't understand the ins and outs, but am happy as I have my laptop back again

I think it involved changing the settings in both the modem and the router - he was impressed that swisscom stayed on the phone while he messed around with it, in a way that Virgin in the UK wouldn't have done.
No idea whether it was free or not to call - he went via the 0800 number.
Thanks again,
Maud