ViewSonic VX2450 sees "No Signal" from 2012 Mac Mini but works perfectly with 2011 Mac Mini

I have two older Mac Minis that have worked well for a number of years, both running High Sierra. The 2012 has been used with a ViewSonic VX2450 since I bought it with no problems. About two weeks ago, the monitor started normally but then showed "No Signal" and went to sleep. I figured that that monitor had died so disconnected it and switched it with an older ViewSonic monitor that I had been using with the 2011 MacMini. The older monitor worked with the 2012 MacMini and, surprisingly, the VX2450 worked perfectly with the 2011 MacMini. I had just switched the monitors and not the DVI cables or power cords. I reconnected the VX2450 to the 2012 computer, "No Signal." So the older monitor works with both computers, but the newer monitor (VX2450) sees no signal from the computer it has been connected to for years, but works perfectly with the older MacMini.

I know these are all old components (but so am I) and all worked well until recently. This one has me stumped.

Thanks!