Most likely a fuel delivery or ignition issue. Check three things in order.
- Ensure the chain brake is disengaged. A engaged brake prevents starting.
- Verify there is fresh, properly mixed fuel in the tank. Old or incorrect fuel is the most common cause.
- Check that the On/Stop switch is in the 'On' position.
IF THAT DIDN'T WORK: If it still won't fire, the spark plug may be fouled. Remove it, clean the electrode, check the gap, and try again. A completely flooded engine can also cause this. Remove the spark plug, pull the starter cord several times to clear excess fuel, dry the plug, and reinstall.
HEADS UP: Always use the inertia-activated chain brake for safety. Let the saw cool before refueling.