Not much to go on here, have you got a cylinder mower? its possible that a spring has come off the carburettor throttle linkage and dropped down underneath therefore the engine will just stop. Otherwise, could it be just an old spring, say from a folding chair, thats lain in the grass till now and it's jammed the blades when you ran over it? try raising the blade cylinder by unscrewing the adjustment screws to see if the spring falls out. Good luck.
crabbiepattie
April 2010