Small Engines (Lawn Mowers, etc.): Lawn mower, crankshaft pulley, self propelled lawn mower

Question
I have a self propelled lawn mower.  the front wheels are propelled.  Last fall I hit something and there was aloud noise and the front wheels will not longer turn via self propelled.  Making it very difficult to push the mower....What is the problem.  Can you help.  the mower starts, but I'm unable to use the propel.

Answer
 Hello Jerdon:

 Is the Ground Drive Belt Intact? Is the Crankshaft Pulley Intact? Block the Mower so the Drive Wheels are Off the Ground a Couple of Inches and Yet the Rotary Blade is Not Exposed. ****REMEMBER THE BLADE IS DANGEROUS EVEN WHEN THE ENGINE IS NOT RUNNING AND EVEN MORE SO WHEN THE ENGINE IS RUNNING****Have Someone Be the Safety Person and Engage the Drive. Is the Input Pulley Turning? Is the Pulley Turning the Input Shaft? Send me the Make and Model Numbers Off the Mower, Please. With these I can Locate the Proper Manual and Better Assist you. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John