That is strange, have you checked to make sure the monitor is plugged in properly and has power? Maybe try unplugging it from the PC and from the wall, shut down your PC, plug everything back in and boot the computer to see if that helps.
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The problem was when I installed a new image on the 2 PC's, it has a multi-monitor card, the default monitor was #2. The monitor output blanked and persisted so I was required to reimage and start over. I restored the image, and did what I needed to get the primary monitor to default to #1. Then everything works normally.
Strange thing to happen but hope it helps someone out there!!