2002 Land Rover Discovery 2 WILL NOT START

IN THE BEGINING THE EXTENDED WARRANTY REPLACE THE RADIO/NAVI CAUSE IT KEPT BLANKING OUT AND OR RESET THE SYSTEM WITH THE CODE IF THAT WAS THE PROBLEM, NOW THE WARRANTY IS OVER, MY PROBLEMS BEGUN. CAR WILL NOT START, TOOK IT TO A CERTI MECH AND HE SAID THE FUEL PUMP WAS BAD, REPLACE THE PUMP WITH A (USE) ONE, AFTER THAT THE CAR START SOMETIMES AND SOMETIMES IT DID NOT START. TOOK IT TO A DIFF CERTI MECH HE SAID THE FUEL HAD NO PRESSURE, REPLACE THE PUMP WITH A DIFF ONE THAT WAS TESTED BY THE MECH, BUT THE CAR STILL WILL NOT START, THE MECH SAYS THE SECOND PUMP WAS GOOD CAUSE HE TESTED IT HIMSELF, HE SAYS IT MUST BE AN ELECTRICAL PROBLEM THATS KEEPING THE CAR FROM STARTING, PLEASE HELP.