Tractors

I have a poulan riding mower. The problem started the other day when the engine started losing power and shutting down. It finally reached the point where it would not turn over. The battery was fine and I replaced the solenoid. The starter worked fine with the new solenoid, but now it is back to the point where I have to use booster cables to start the machine and the losing power/shutting down problem still exists but not quite as bad.

Help!

Any help is greatly appreciated.