I seem to have spent most of yesterday trying to recover from one PC
crisis after another. My final problem was that on switching to three
screen mode, the left hand monitor stayed blank. I'd had this problem
initially, so when I cured it I saved a named System Restore Point.
Only, after the shennanagins with the system ruining Nvidia driver
update, none of my named Restore points had survived.
It was just after I'd kicked off a restore to Saturday's settings that I took a closer look at the recalcitrant monitor. I hadn't switched it on.....Doh.