The old floor is damaged and is probably not salvageable. I don't know how you could make it look satisfactory. You can install new floor (prefinished or unfinished) at a reasonable cost. Match species and style if preferred. Older floors were commonly 2-1/4 strip oak. Material costs for unfinished are under $3 per square foot. Since you have refinished the other floors, the initial finishing should not be too different except you may need to use some filler.
The hard work is going to be pulling up the old floor, starting with the removal of all those screws. You can rent a nailer where you buy the flooring.