It was odd. The cursor arrowhead was still stuck in the same place after rebooting -twice.
Looking around in devices and the like was made impossible. I could pick the device, but not get into the driver screen for example.
Java flashing away on the Task Bar was the clue.
After half an hour of trying a bit of this and a bit of that...i.e. stabbing in the dark, allowing the install to finish made everything come back to normal (I hope)
One thing: Just prior to the crash, the entire (Netflix) screen grayed out. I've seen this before, but last time I got it back by random prodding, or simply chance. This time, it was the end of the Windows session.
Windows recognized the fault and put a DOS type screen up telling me something - implying hardware - had probably gone TU. It then took me through 20mins of trying to repair or diagnose the fault. It said sorry, but it couldn't. Would I like to report it.
I was just shy of board-stripping when the Java thing showed again.
I ran it for quite a while after the event, I'll try it tonight and see what happens.