"new"grape Imac

Bought a new to me Grape IMac, want to set it up to play some of my old favorite games I used to play on my bondi-blue rev B Imac, with maxed out RAM. When I power it up, screen looks good, but get folder with the flashing question mark. I bought software for os 9 install and 9 install software, now get "problem, catalog file entry not found for extent, 4 - test done, but disk first aid can not fix them. What is the next step on this? Is this likely because the original PRAM battery or whatever is dead from age, or ??? Intend to put this into the shop to service it, max out ram, but would like to know what I am looking at - I think this is a 333 if I remember right -