1989 mazda mx6 stalls?

It ran perfectly, then all of a sudden it just shut off and wouldn't turn over. It starts up again after a while. I've been starting it every morning just to see and it started perfectly, only now this morning, the engine was knocking, when it first stalled and i tried to start it, a lot of smoke came from the exhaust it was like a black blue mix. blue smoke has been coming from the exhaust a little but only when accelerating and it ran fine anyway, someone told me that means there's a burnt piston ring. if that is the case, would it burning more make the car stall completely? and why did it all of a sudden start knocking?