OK, after saying my OH had upgraded from 7 to 10 without any problems, he's now got problems after his PC went to sleep.
Problem solved, somehow he'd got his PC set to Tablet mode. I've left the problem he had below in case it happens to anyone else. If you go to Settings, System, Tablet mode, it needs to be turned off for PCs, there are also 2 other options, When I sign in, choose Remember what I used last, or Go to Desktop, his must have been set for Automatically switch to tablet mode, and the second option is When this device switches tablet mode on or off, there are 2 options. He's now chosen "Don't ask me and don't switch".
1. He's lost all the icons that were on the desk top. In fact the only thing on his desk top are some of the app icons, that should only be available if he right clicks on the Windows icon.
2. Whenever he opens Mozilla, or his e-mail provider everything covers the page. The box in the top right hand corner doesn't work, neither does clicking on the edges and making the page the size he wants, in fact he can't even do that. What happens if he clicks on the side is that everything just moves to one side of the screen.
He says he's not touched anything, so what has happened? He has just rebooted to see if that had any effect - it didn't.
Modified - What seems to have happened is when he clicked on the Windows Icon the page that comes up, showing apps etc. has stuck. He can't get out of that and even when he tries to open Firefox or other programmes they fill the screen. The odd thing is that I tried it with my laptop and as soon as I opened Firefox, I got my desktop screen back and Firefox opened at the size I like it.