If the pull cord is tight at all, do not keep pulling or you risk damaging the pull cord.
Remove the black cover cap from the motor and rotate the big outer nut on the end of the shaft using your finger and thumb. Check that the drum is rotating freely in both directions and ensure that they aren't any blockages.
If the drum is not moving freely using your finger and thumb, then remove the hopper and clear any blockages from the drum, spinning it back and forth using the nut on the motor to ensure that the entire drum is clean of any possible blockage.
Position the hopper back into place and tightly secure the bolt. This is a crucial step as the bolt acts as a safety mechanism for the chipper . Also ensure that the correct bolt is used when reassembling.