If all you have in there is live sand, then you won't have anything to "start" the cycle. The cycle is bacteria turning Ammonia into Nitrite and then Nitrite into Nitrate. Right now you have no source of ammonia, so any bacteria that did come with the live sand has nothing to consume. It's like not eating for 3 days and then wondering why you don't have to poo haha. Because you haven't eaten anything. In this case, the bacteria in the tank have had no ammonia to be eating, so nothing is happening.
My advice that has worked in the past, is supported by general best practices in the community, and that I'm doing right now on a new build, would be to go out and get some rock in there, either live or dry. They each have their pros and cons and a quick search on the forum will have tons of good threads. Then get a bottle of Dr. Tims or Bio-Spira. I prefer Bio-Spira because it's much easier to get locally vs having to order online, but either will do. Add this to the tank and then do one of three things in my order of preference:
1. Get some pure unscented ammonia and add it to the tank to get your level up to 2ppm each day. This will directly add ammonia for your bacteria to feed on and start your cycle. I think this is best because it gives you the ultimate control of how much ammonia goes in, so you can see exactly how much is being converted.
2. "Ghost Feed". This means feed the tank whatever food you normally would as if you had a few fish in there. The food will break down and release ammonia. This is arguably a bit slower because you have to wait for the food to begin to break down.
3. Drop in a piece of fresh shrimp from the grocery store. Many people have a lot of success with this. You drop it in and like ghost feeding, wait for it to start to break down and release ammonia. I personally do not do this because the shirmp can get smelly and I'm stuck pulling out a half decomposed shrimp carcass later. No thanks.
Then monitor your ammonia and nitrite levels daily. Once the tank can take the 2pmm of ammonia you're adding or the ghost feeding and reduce it to 0 ammonia and 0 nitrites within about 24ish hours, you're good to go.