Lost compression?, did you verfy this with a compression tester?. If so, remove the valve cover , check and verify that the rocker arm did not slip off or partially jammed in an akward position that would keep the valves from closing. Check the valve springs and keepers , make sure the springs are not broken. If all that checks out good, perform a cylinder leak down test and determine if the loss of compression is coming out of the exaust, intake, engine crankcase or head gasket.