BT engineer came out today (3rd time) and seems to have fixed the problem: OK on tablet and phone. PC says 'no Internet connection'.
Ran Windows diagnostics -' connect ethernet cable.' There is a loose cable, but I thought WiFi didn't need ethernet too? If it does, where do I plug it into, please?
Thanks everyone
I was so fed up with the whole business that I contacted BT yet again - heaven knows what they must think of me - and was advised to plug in the ethernet cable. As if by magic...well, it wasn't the shopkeeper but it was the internet (apologies to anyone reading this under the age of 50). He seemed to be saying that now it's switched on again I can remove the cable, but as long as it's not costing me anything extra(?) I may as well leave it in?