Ok, thanks for your advice, Magic Banana. I will give that a try, although I
am using LXDE, so I'm not sure if that same option will be in there. It's a
second-hand laptop that is a few years old, so it is quite possible that the
HDD is old and may be defective.
So, if the hard disk checks out ok, would you agree with the following plan?:
- Back up the contents of the root partition
- Re-format the partition to renew the filesystem
- Re-instate the system from the backup and see if that solves it