Lisa, I haven't the money or time right now to sand all the floors ... and want to wait until the other major projects are done first anyway. In the meantime, I have found a machine put out by Koblenz that will lightly sand my floors to take off the old wax buildup, and the black discoloration you spoke of. This machine will also buff the wax for you too. After having taken up carpet I discovered really dry wood with too many splinters! This machine has really helped in removing the splinters and wax buildup that was surrounding the outside of the carpet, and really helped get the oil of the wax into the wood where it needed it. You may find another brand machine where you live, this is just the one I found that is for home usage and won't kill me physically to operate. Hope this helps. Several restorers around here had advised me to do this until I was ready to sand and refinish.