Replace them. It's time.

You might be able to do another sand. Depends on how much wood was taken off the previous times.

Replacing is the expensive option. Call a pro out to hear all your options before you maje a drastic decision.

Thank you. I found another website on this subject which recommended using a fine steel wool and Restore a Finish, then cover with Johnson paste wax and buff. I tried a small area and it looks great. Thank you

Another option would be to hire a floor refinisher to clean with mineral spirits, treat the floors with Dura Seal Renovator and buff with fine steel wool then apply paste wax and buff. It's probably similar to the product you mentioned. Wax and buff again in a couple weeks then in six months. Do high traffic areas as needed then clean with mineral spirits, apply wax and buff once a year. Lower traffic areas won't need as much attention as high traffic areas. Once you get a nice wax patina you'll be able to buff out scuffs and you can switch from a paste wax to a liquid wax (NOT self-polishing wax) that will dry faster and buff up nicely.

They didn't used to have all of those commercials about "dull, yellow, waxy buildup" for nothing. Wax is a PIA as a floor covering. Sand it down and put a decent hard coat on it if there' enough depth of wood left.