How Can I Get My Mac Back Into a Working State?

I just happened to run into something this week, and a, that was, i was on tue's official help pages. I don't know how anybody could make something like this, because i get confused every time. Long story short is, who knows why, but for some reason i was able to get the old one to boot again. But my policy on this stuff is, i just do not trust a computer when that kind of thing has happened. It has failed. So even though i did get that computer into a working state, it has done the shuffle down progress in our house - we used to have a very old, non retina imac that functioned as our computer