The fuel pump can lose its prime like a water well pump. Pull the hose from the tank to the fuel pump and make sure it runs a good stream. Pull the hose from the fuel pump to the carb and make sure it's not plugged. Pull the bottom reservoir off the carb and make sure it's not full of stuff. If that reservoir is full of things that look like dead ants, you need to replace your fuel hoses.
Hook the fuel hoses backup and put the tractor nose down. If the hoses are clean and the carb is clean and it still won't start you need a fuel pump.