I have a 2007 650 bmw i somtimes the doesnt start

Check crankshaft sensor and cam sensor,check fuel filter.

no voltage

could be battery flat or loose terminals
alternator
start motor
engine bay fuses or relays

next to check os immobiliser

if you cant sort it .. may need a tow to the bmw service center

Yes it could be your fuel pump

Certainly sounds like a lack of power in the battery.
Do you have a genuine BMW battery or a cheapie replacement?
Have you tried to jump start the vehicle.
Batteries can seem ok, but when called upon, the power drawn out of them can be insufficient.
Try charging battery and starting on the charger- or just jump start to see what happens

i had this problem with my 1990 316i and had to replace the fuel pump. the pump can be expensive but with a little doctoring with the return pipe a cheaper pump will do. hope this helps

Check your electrical system for direct shorts. Move the wires/cables around and see if you can get it to happen while idling in neutral in your driveway.

repalce bulbs first and clean contacts where bulbs go into socket. report back

lockup torque converter solenoid will cause this

HI it just sounds like a faulty airbag sensor, these are common on all bmw's try getting the local dealer to reset it or alternative is to replace the sensor,
Hope this helps
Steve

my cruise control and the controls on the steering wheel are not working, Just picked up my 2005 BMW Z4 from the dealer. Where do I start Looking to solve the problem.