By alarm do you mean the ign buzzer as this will operate as soon as you turn the key to ign on engine not running once engine is running should go out .
reasons for buzzer to make a noise whilst engine running are hand brake on and machine in forward or reverse ,low battery charge rate will also put battery icon on dash panel , low trans pressure also light on dash panel , low engine oil pressure and light on dash, air filter blocked and light on dash, i think also there is a temp overheat as well.
As far as you fuel you need to perhaps start with the basics at tank firstly by checking the tank is clean in side and that no floating debris also that the fuel pipes are not blocked in any way check each one in turn perhaps blow an air line down each to confirm.
Fuel sediment trap if its the one with a plastic bowl with a 10mm nut on the top check that the o ring is under the nut and also the square section seal is in good shape as these will draw air in as they are on the suction side of things (but don'
t over tighten the plastic bowl or it will pull the threaded rod out of the plastic )
As far as any shut off unless the machine has an immobilizer fitted and you have power to crank and start the machine and you have 12 volts to the stop solenoid on the injection pump your in business the stop solenoid some times fail you can pull these out and check the plunger pulls in when ign is turned on and released when its turned of the electrical terminals if old used to give pore connections may be if suspect crimp some new spade terminals on.