Followed the possible solution and logged in asd administrator, but it has not cleared the problem.
I think I’ve cracked it! When you had Libre Office installed in Windows 7, did you have the program set to 'Run As Administrator!? I did and didn’t change anything when I upgraded to Windows 10.
I upgraded again earlier and then I went to the .exe for Writer and told it not to ‘Run As Administrator’, I then did likewise for the shortcut and I can now open files just like I used to.