The first time you ever see your tarantula moult can be quite frightening... it looks dead on it's back!
As a rule, when a tarantula is lying on it's back it's
NOT DEAD, it's moulting instead and should not be bothered!
When a tarantula dies it almost always dies in a death curl or right side up at very least

.
Indications of an impending moult would be a large abdomen, the tarantula no longer accepting food , excessive drinking, and last but not least, if your tarantula has a bare butt (hairs flicked off), the darkened colour of the 'skin' will be a perfect indication of a moult within hours to a week or two.
Firstly if it's lightly coloured it means it's far from a moult...
But if it's gone dark it means that there's brand new hair under there and a moult is imminent....