Second monitor in "power save" mode since Windows update

This morning Windows did an automatic update and when it restarted my tertiary Dell monitor will not work. It works fine on another laptop, just not on my Toshiba.

When un and replugging the Dell monitor I get a message saying the monitor is in power save mode and to move my mouse or press a button on my keyboard, but I'm already seeing my second monitor working fine.

My set up is this:

My Toshiba laptop is kept closed with its monitor disabled under Control Panel/Display.
My main monitor (Display Number 2) is a Samsung plugged into my HDMI slot.
My second monitor (Display Number 3) is a Dell, which shows up as a generic P&P monitor, plugged into my VGA slot.

The mouse moves off the Samsung but there is no sign of it on the Dell display. I have plugged in a different monitor and have the same problem.

I've tried un-installing the Dell monitor then replugging it, which then gets added to my device list as both "generic plug and play monitor" and "generic non-plug and play".

Any suggestions on how to get a picture back on the VGA monitor?