Not sure how best to describe what has gone wrong, and I certainly don't know why!
Normally, when looking at This PC, which used to be My Computer, the screen is divided, with a tree on the left and the contents of each branch on the right. Suddenly, the tree side has gone, and what was on the right now occupies the full screen.
I've Googled until cross eyed, and searched every menu known to man, but cannot get back to how it was.
Any clues?