What is wrong with my 2002 yz250f?

i was riding. good on oil and it died, but did not instantly lock up, and it made a funny sound as i rolled to a stop like a rattling sound. and i could not kick start my bike. i checked the oil and it was good. got home and was really low on the dipstick but i cant find the leak. i think my cam chain came apart and my piston smashed the valves.... any ideas would help allot my motor is now seized up