I recently bought a John Deere F725. I was mowing with it and it was going along just fine. Then I shut it off to put more gas in (had sent someone to go get more while I began mowing). When I started it again, it fired up, but the mowing deck would not engage when I pulled the yellow control switch. I shut it off and took a look. The drive belt and mower deck belt had both slipped off the pulleys. I got both back on just fine. I figured that was the problem, but when I tried to engage the deck, again the blades wouldn't turn. The mower starts and goes, but the drive belt for the deck underneath the mower won't even try to budge. I'm assuming it's an issue with the pull switch. Anybody have a better idea as to what the problem could be? ( and no, I don't have the parking brake on)