When I take a screenshot on my mac mini it turns up white
I am using Mac OS High Sierra on a 2011 Mac Mini and every time I take a screen shot (command+Shift 3 or 4) the image turns out blank/white. I have tried opening using various programs and always white. I have rebooted by mac several times. This is only a recent development in the last 5-6 months. All my other macs work perfectly. I checked the shortcut keyboard keys in preferences and the boxes are checked. I also restored default settings. Anyone have anything else I could try or have the same issue. Please help.
Mac mini, macOS High Sierra (10.13.6)