Lawn Boy 10687

I've got a Lawnboy insight I believe 4cycle with the BCS engage. All of a sudden when I go to engage the blade it kills the mower. Mower runs perfect but mashing the bcs switch kills it unless I let off of switch the goes back to idle. Any help be appreciated it's a good mower. Thanks

Check the engagement belt, to me it sounds like it is off and freezing the system. When was it replaced last?