BMW X5 2004 4.4i

If possible get a basic volt meter and see what the voltage is at the starter lead with the key on. If there is power there it is possible to bridge connections there to bypass starter and if it starts then you know starter most likely is the problem. If there is no power with the key on then have a look at fuse box under hood, it may be labeled accessory/starter usually under the fuse box lid there is a diagram of what fuses go where. Good Luck!