DIAGNOSIS The chain is on backwards. The cutting edges are facing the wrong direction.
FIX Remove the bar and chain. The cutting teeth on top of the bar should point toward the bar tip. Reinstall the chain so the sharp edges lead into the wood.
IF THAT DIDN'T WORK The chain brake could be partially engaged. Ensure the front hand guard is fully forward and not contacting the clutch cover.
HEADS UP A backwards chain will ruin the bar rails and overheat the motor. Always check direction after sharpening.