Booting PowerMac G3 desktop

I have an extensive library of valuable musical compositions by a friend who died in 1997. I've been using his MAC since to print music as needed, but last year his notation program, Composers Mosaic, went corrupt. The software company, Mark of the Unicorn, went out of the business of notation software long ago, but were kind enough to send me a CD with the last version of the program. My friend's old MAC does not have a CD drive.

So a friend gave me a Powermac G3 desktop, which worked fine when we took the components apart at his place. Now, however, at my place, it does not boot. The cursor appears on a blank screen and the mouse moves the cursor, but that's it.

I'm using a model M2980 keyboard and a Kensington ADB replacement mouse. Do I have a compatibility problem with these units? The monitor that I was given is not a MAC monitor; is that an issue?

Any advice?

Given the age of these computers, my goal is to get the program up and running and print everything so I'm not dependent on aging hardware to preserve the music.

Thanks.