Two Monitors

[KennyR]

There's no danger with power, since monitors don't draw any real power from the computer itself.

It's this that's bad:

Also, when software needs 15khz screen and I switch on 19834 monitor, the PC monitor displays the expected out of range message; is it bad for it to be continuously receiving a signal that it can't display

Yes, it certainly is bad for it, as is switching it off constantly.

Not really an appealing suggestion, but you could get a scandoubler and monitor switcher and use just one monitor. This is how I handled this problem. Expensive though.

[KennyR]

Most monitor switchers are mechanical. It's just a big clunky rotating switch on a box. They degrade picture quality a little too, especially if you get long VGA cables.

Some monitor switchers are electronic. Eyetech's MON range are operated by a toggle that can be mounted on the front of your tower and is powered from a 3.5" powerfeed inside. This one is a lot better and won't lose much quality.

Finally there are monitors which have switchers built in, usually top-end ones like Ilyama.

But in all cases you'll have to do the switching manually.