Four mechanics can't find problem

[Rafael Gonzalez]

My 2001 X5 3.0 will start when it wants.Sometimes it starts right a way for a week and sometimes for an hour.The car cranks and sounds like it's going to start,but it does't,you keep trying for 15 min. to 30min. then it starts like nothing happended.Then it will work perfect for 3 days or a week maybe more,then samething happens again and it can do it everytime you try to start it,the car has gone thrue 4 mechanics wich I believe they are trial&error mechs.They have change fuel pump,computers and everything they ca think of.I'm starting to believe it could be injectors or electrical,because once it starts it runs great.I would like to get some feed back before I keep spending more money.Thanks to anyone that can help me out,RAFAEL.