Thanks torvic for your advice.
My son volunteered to have a go at trying to fix the SSD. As the SSD was made by Samsung he looked on the Samsung website and found some diagnostic and erasing software to download. Unfortunately this is one of those times when you can only use a MS PC to perform this. The diagnostic software found that the SSD has only had moderate use and no obvious problem so a complete erase was the only thing left possible to try.
So I have just re-installed Manjaro Cinnamon and it seems to be running ok. I will see how it goes. Pity there is no way to use these tools in linux.