Pete in Holland MI
Take the belts off.
Does the arbor rotate? If not, probably siezed bearings, or maybe a pulley has crept on the shaft and is wedged against the housing.
Does the motor rotate? If so, turn it on and give it a spin. If it takes off, the centriphical starter switch contacts are dirty. Blowing them out usually cures the issue.
Let us know what you find !