I've tried your suggestions Spurlash2 (except the link, which I'd already got from another forum and it didn't work). Not sure which of your other procedures had the effect, but on restarting my PC just now I'm getting maximum windows every time (so far anyway, fingers crossed).
Stilll confused, but something's done the trick, just wish I knew what it was.
Wonder if it's one of those Windows thingies that eventually responds to repetition?
Many thanks to Tarq57 and Spurlash2 for the much appreciated input.