I'm no expert, but I pulled up my carpet and redid the hardwood floor in my second bedroom. It too had stains which came out when I sanded the floor. I rented a large floor sander but you have to be very careful so you don't burn the floor by sanding it too close. I then put three coats of polyurethane down. I was surprised that it came out so nice. I prefer the floors to carpet because I find them easier to clean, especially with the new products like "Swiffer". It is a lot of work. Make sure you use a face mask to keep out he dust. Good Luck!