What is wrong with your car if the engine makes a screeching sound and shuts off while you are driving?

The harmonic balancer for the engine may be worn-out or loose, check it out! The noise is likely to come due to the friction.

Blaming the harmonic balancer for this problem is a real reach. The belt is slipping. Tighten the alternator to tighten the belt. There should be less than 1/2 in deflection(amount the belt moves when you push lightly on it) if that doesn't help much, change the belt. Sometimes if they have been slipping for a while, they build up ma glaze on them that will continue to allow them to slip[ and squeal.

Sounds to me like a main or connecting rod bearing seized. If the engine now fails to crank over when you try to start it, it's seized.