Lifeless crab, don't assume death!

Its unfortunate that hermit crabs pull surface molts, but unfortunately some do, for no reason. you can ahve the perfect set up, and find a crab lifeless. I know this is going to sound odd, but it's important you smell the crab. If there is an unstakable horrible odor of rotten fish, your hermie has passed on. If you smell nothing, or smll a slight chemical smell, your hermit crab is pulling a surface molt in you.
Examine the 'body' again. Can you see the black eyes on your hermit crab, or does that area look 'empty'. If there are no eyeballs there, then that is not a body, it is an exoskeleton! The crab is probably white and pulled far back into the shell, hardening. Never remove the exoskeleton. Once the hermits mouthpeices have hardened enough, they will eat the exoskeleton to regain enough calcium and other nutrients to finish hardening all the way.
If you do see the eyeballs and smell nothing, or a faint chemical odor, then just wait. Moving the crab to an isolation tank is just to stessful in my opinion, and can raise the chance of death. What I do for a surface molter is cut off the bottom of a 2 leiter plastic soda bottle, and push it down into the substrate over top of your molter. This way hermie can not burrow and reach the molter, or get to the vunerable crab. Once the hermie has finished eating the exo and is fully hardened, and moving around, you can remove the bottle and let the crab back into the main tank.