Xterra won't start if not cooled off?

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My 2000 Xterra won't start sometimes...seems to be if it has not sat and cooled off enough. All lights come on, but when you turn the key...nothing! No noise nothing. Have found no loose wires....the starter does get very very hot...is this normal? Mechanic pulled the auto start and security system out 4 months ago, due to car not starting. Seemed to do just fine, but now the weather is warm. Help! Thanks