I have a Simplicity riding mower and the deck fell off it while I was mowing so I put it back on. I hooked it on the front and the back. The belt is on correctly. Whenever I started the mower I pressed the accelerator but the mower would not move. The brake was not on. What is wrong with it?

Make sure the deck didn't knock the drive belt off.
Didn't say what model it was , if it's a hydrostat make sure the release lever for the hydro is in.
Luck

Thanks DG it was the release lever.

Your welcome.

Simplicity tractor won't shut off