My hermit crabs are not sleeping during the day?

My hermit crabs usually sleep during the day and come out at night but this morning the i found them all sitting out :S I mean they look fine but they do not ever come out during the day! My one crab has done this for two days now. It's so weird! And they don't even get scared when I come near the tank anymore?? What's wrong?? there are two heaters under the tank...could they be too hot?? I just cleaned the tank like last week and but they just started doing this in the past few days, they have always been fine with those heaters...what's up with them??? Especially the big one that doesn't ever go back in the sand?? I am worried :( Thanks!