In order to give us a clue, you have to define “not starting”.
When you are in this type of situation…does the starter turn the engine…or do you hear nothing when you turn the ignition key?
Apparently, I am not the only one who is confused by the description, because one mechanic replaced the battery (which means that he apparently thought that there was not enough electrical energy for the starter to turn the engine over), and another mechanic replaced the fuel pump (which means he apparently thought that the engine was turning over properly, but not getting fuel).