First of all, a clock (or watch) can only have been "wound too tight" if the mainspring was broken in the process. This would require considerable effort towards the deliberate destruction of the spring. Having said that, I suggest you look within the movement for a physical obstruction or possibly some issues with the suspension spring, rod, or pendulum. There is a special tool for unwinding clock springs. A pawl lever that provides the "ratcheting" sound during the winding process must be lifted when the hand-grip tool is used. In some instances the movement must be removed from the case to do this.

A closing word of advice: NEVER attempt to unwind a clock mainspring of ANY kind with the winding key.

Regards,

Max Stout