If you are driving and you over heaet your car.

You could crack the cylinder head but that is much less common than warping the head. A warped head can cause a coolant leak and overheating, and overheating can cause a warped head.

First you have to determine the cause of the no-start. That can mean a lot of different things. If the starter doesn't even crank the engine there could be something pretty serious wrong, especially if you drove it a good distance with it overheating. If it cranks fine have the no-start diagnosed first.

I have no faith in chemicals to magically repair a leaking head gasket. At least I haven't heard anything good about them so far.