YTH 150 Mower/ rider?

I am trying to get the drive to work. It stopped while mowing and the machine does nothing when you try to back up, try to go forward and it fights you and grinds but if you push hard enough you can engage it but the machine does nothing. I took it aprt to access the transaxle to add some oil, but cannot find a plug so this one must be a sealed peerless. Would changing the belt help this issue or do I have bigger problems than a simple repair?