More than likely you carburetor may need cleaning/rebuilding and fuel tank needs cleaning as well. You could confirm this by giving the engine a direct capful of gas down the carb throat and try to start it. If it fires off and then dies it is most likely what I said it was.

i will try this thanks

Further to what RD advised if tractor turns over and fires with fuel through the carb throat . Have you listened , when you turn on the key for a Audible click ? I believe your model rider has an electric fuel pump . If u do not hear click or hum the fuel pump may be faulty or bad wiring connectors or fuse . You could verify by disconnecting discharge line from pump and turn engine over to confirm it is pumping fuel to the carb . There is sometimes an inline fuel filter upstream , either within the fuel tank or the prior to the fuel pump and carb . This also could be restricted .