I will try this tonight.
I can use the LCD, but only intermittently. I checked the settings when the LCD was and it was on 70Hz (or maybe 75) and couldn't be changed.
I also checked the settings when the CRT was displayed and it was set to 60Hz.
The issue often goes like this.
Change user or other event
Display goes blank
Plug in CRT
Signal is there
Plug in LCD
Signal is there too, for a while, until the next event.
I left PC on last night, all night and LCD was still on ok this morning. It seems to be when Windows re-evaluates the display, I ignorantly guess.