Answer: Basal rot is generally a result of overwatering. You can avoid this problem by watering less and by covering the top of the soil with a thin layer of chipped stones to keep moisture away from the base of the plant. You should be able to salvage your plant by cutting off a healthy stem or pad, allowing it to air dry for a few days (to a few weeks, depending upon thickness). Once the cut has calloused over insert the base in a peat-based potting soil. This is best done in spring or summer, but you might have success now if you provide heat and light during the day.
Allow the soil to dry out between waterings, especially in the winter time when growth slows.
Good luck with your cactus!
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