Stopped while driving and will not start

My vehicle (6.2 liter) came to an complete stop while driving, my temperature gauge did not go to overheat. As I pushed the gas the vehicle started idling down to a complete stop! Had to be towed home, the tow truck driver placed a laptop machine looking device on the vehicle. He stated it was my timing chain. Another mechanic stated yesterday that the timing chain is working however it sounds like something is broken on the driver side. He called it a rolling gasket or roller (IDK) excuse my terminology. I am a female and I do not know much about vehicles. The part he is speaking of, I have 2 on the left and 2 on the right. The 2 on the driver side is not working and the parts cost $250.00 a piece. The vehicle has not started since it came to an complete stop, I have had this vehicle for a year so I do not know what the previous owner did with the vehicle as far as maintenance before I purchased it. Can you please help me?