I dont wanna bring bad news but, I had an old maroon car that wouldnt fire kept cranking and cranking and then it just stopped and the next key turn the starter started to click and the car wouldnt turn over.
The engine was siezed up. The #3 piston top was completely melted off (so much for "only overheated") and a chunk had stopped the motor by wedging itself between the crank and the block.
Im not saying your motor is doing this but id get a flashlight and maybe take a peek, My experiance acted just like yours.