Done! I decided this time to use the free Microsoft Essentials Security, which is nice and simple and won't try to flog me upgraded versions. What peed me off was when I was asking AVG 2011 to Uninstall, it announced that I still had 945 possible threats on the pc. So where the hell were its hitmen? Anyway, just Installed and Run MES, which tells me there's nothing nasty in the woodpile, so all I need now is AVG to honour their 30-day moneyback guarantee and reimburse my £42.99. Everything is going at proper speed now, with screens getting populated without waiting for the kettle to boil!
As always, folks, thanks for insights and advice. Always appreciated by a pc numpty!