Will not start

Alright so, my friend wanted to learn how to drive manual. He drove it perfectly fine until he reached a stop sign, he then proceeded to let go of the clutch, but forgot to give it gas as he released. The car was about to stall but then he stepped on the gas and the car jumped to start and it did like a back and forth motion of turning off and on while moving at least ten feet before smoke came from the front and then the car would not start whatsoever. I thought it was the head gasket seal could have been broken, I replaced them. I checked the timing belt didn't jump a tooth. I'm now wondering why the car wont start.