Land hermit crabs are nocturnal, so they sleep during the day and are awake at night. The best time to see your crab in action is late at night. Stay up late one night with the lights very low and see if your hermit crab is busy exploring, eating and drinking. If he is, then all is well and your crab is perfectly normal.
If this is a crab you’ve just purchased and brought home, he may be destressing. Land hermit crabs endure a great amount of stress before reaching the pet store. The harvesting and shipping of crabs is a very inhumane process and the crabs suffer because of it. They then arrive in pet stores, who in most cases, dont know how to properly care for them. They arrived stressed out, dehydrated and hungry. Then you purchase them and take them home. At this point your new crab will often dig down into the substrate or find a hiding place to recharge its batteries. This is a way for the crab to try to recover from the damage its suffered. This could take a week or two weeks, depending on the crab. Often it takes a period of time for the stress and dehydration to catch up with them but it does and the crab dies. Sometimes its a week, or a month but it could take longer. Gill damage from dry air (lack of humidity) can be a slow painful death for a hermit crab.
If your tank conditions are optimal and your crab is still inactive, there really is not much you can do other than leave it in peace. Handling your crab will not make the situation better, in most cases it will make it worse. If you are handling your crab to see if its still alive, that is unnecessary. If your crab does indeed die, you will smell it.