I hadn't tried that, Tigerwolf7. But I have now and it makes no difference.
BTW, this morning there's no beepy noises when I try to power up, whatever's connected - just the green light and the quiet noise of the fan.
Thanks Mary G
I was looking at the silvery shiny sticker on top of the PC case, but have since seen a normal black on white printed sticker on the back of the PC case.
I'd emailed them, but I'll go in again and try chat.
Got there thanks. You were right - I had to take out the memory and replace it, then it all worked fine.