Did the Windows Update include an 'optional' video card driver update? If so I would guess that the driver changed the way the system handles extra monitors.

There is a general rule that we don't accept Microsoft offers via Windows Update for driver updates. They never did them well.

The easiest option to is to System Restore back to before these updates were installed. If that works, you will be offered the updates again but look out for any optional driver updates and refuse those.

Mark