If it were mine, I would toss the sand, then mix up some new saltwater and scrub the rocks with a scubber brush. Then I would "cook" the rock (link to directions in my signature). Once there is no more ammonia in the cooking rock (probably 2-3 weeks) I would add a small "fresh" uncured piece of live rock from the LFS to seed the old rock with some new life. Once the rock has been cooked, which will take probably 6-12 weeks total you can put it back in the tank with new saltwater, powerheads, whatever you want for equipment, then after a week add some brand new sand (rinsed well). The live rock will make the sand into live sand after a short while. Let the sand settle for a week, and add your first fish/coral.
In the future, if you drain the tank and store the live rock in a bin with saltwater, a powerhead, and a heater you can keep it indefinitely if you feed the rock a piece of shrimp once a week or so. The size of shrimp would vary according to the amount of live rock. I would say one of those tiny cocktail shrimp per 40-50 lbs of rock. This will keep it alive.