Okay, when I have time. On the "on/off" button issue, I have had two different desktops since 2001, so I'm no novice, and their buttons were easy to find and I never had a problem with them, which is the difference. This isn't normally a problem. Furthermore, on the first one I had, I do vaguely recall going into BIOS for something or the other. But I also read that you need to be confident that you know the score before going that route.
Although it's been mentioned before, I am punctilious about switching the PC off through Start and Turn Off, so that's definitely not the cause.
Trying the run this repair disc. I had "assumed" (always a bad idea) that I click on the contents and then it would go off and run. There are two folders, "Boot" and "Sources" on the disc. When I click on either, nothing happens. So how do I run this?