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Display suddenly changes (size)

For no apparent reason (surprisingly not an update breaking things), your display size/resolution changes and now shows only a few resolution settings, none that work properly with larger monitors.  You'll need to override the Available monitor list.  In Display:

• Click Display adapter settings (lower right)
• Click the Monitor tab and there, uncheck the Hide models option
• Click Ok then click to the Adapter tab (lower left)
• From the now larger list, select one that works for your monitor.