the pram battery seems to be a MUST with old powermacs. Especially the PCI models. Generally, they won't show screen, but there are a lot of other things that can happen without a PRAM. Worse case is that it doesn't boot.

I think you need to get a PRAM battery before you proceed. The PRAM battery is kind of a MUST on a mac pre-G3 era. So yeah, go ahead and get one

You might want to see if you can use an ATX PowerSupply and see if it's the PSU that went down on the machine. As far as other things, I don't know what to tell you.