My 580B can not even move!!!

I am new as backhoe owner. I just bought this for my yard project. I feel it was very weak to move up on to a hill before. I had to push the fuel padle all the way down to drive it up. Yesterday, I tried to start it, it won't move either forward or backward no matter which gear. But the loader and hoe work fine though. I am trying to fix it myself, but no idea where goes wrong. Thanks for anyone who can help!

My 580B can not even move!!!