Why won’t my used lawnmower go forward or backwards?

I purchased a used toro 10-32 recycler ride on. Model number 56190.Forest Gump type lol. The guy said it needed a starter and battery. It has a pull start so I pulled it and started running.Engine Runs tiptop. I did a couple laps around the bark yard and then it made some clunking noises and stopped going forward. Managed it to reverse though. Reversed it back in garage and just made it as reverse stoped working too. So I replaced the belt and tightened up the chain a bit. Did a test drive and same thing. Any help with this would be greatly appreciated.

Todd