Turns out the operating system works fine, just that I missed the fact that the hard drive was disconnected. Derp.
Anyway, it runs! I set it up next to my real PC. Progress, people. This is twenty years of progress next to each other.
As far as the other PC is concerned, it’s been gutted. I may put it back together since all the parts, including the case, are in really good shape. It had a purple motherboard!