Bmw 525i wont start no starter action battery ok

that happens
what work has been done on the car recently

check battery cable to starter is sound
tight battery terminals
if starter motor clicks ..flat battery

if starter wont turn at all
possible faulty starter
or immobilizer is still activated

Check battery and connection.

check battery terminals sande clean and earth cable to engine clean and good contact >>>>>>>>>>alternatively jump start battery with jumper cables ,if still no response ,can only be starter motor solenoid fault/starter brushes

This is typical of two more common problems; a weak battery (12 volts when not cranking the engine isn't enough) or corroded battery clamps or terminals. Probably #3 is a corroded starter or solenoid terminal.
While cranking, the starter draws from ~120-200 amperes of current and any even mildly corroded connection in the path will drop all of the voltage. 0.1 Ohms of resistance will drop nearly all of 12 volts when trying to start.
Check voltage across the battery terminals (not the clamps) while cranking, not without a good load drawing current. If you have less than 10 volts, most cars will not crank but only cause the solenoid to chatter (=clicks).
If you disconnect the battery for any reason, disconnect the negative (ground) cable FIRST to avoid accidentally contacting the positive terminal and ground with a tool which may melt and/or damage the battery.

if the clicking sound comes from the solenoid when you try to start the engine the solenoid may need replacing, the solenoid is like a big switch that takes the power from the battery to the starter motor,inside it there contacts that come together to make contact & that is where the problem is.....hope this helps.....cheers

sounds like a loose connection to starter motor not allowing full power to solenoid which is where power lead connects. or if it is a second hand starter could be faulty solenoid

sounds like battery or bad starter

Check the transmission neutral start inhibit switch is not the cause of your problem. (try both 'P' to 'N' positions).
If the headlights work ok there should be enough power in the battery to at least make a solenoid type noise when start is attempted- so it may not be caused by a faulty alternator.
Check the battery terminals are clean and firmly attached to the battery,
Check battery is properly grounded to the chassis and motor,
Check that +12v is available at the starter motor engage solenoid when the ignition switch is held in the 'start' position - check any start slave relay operation.
If all above is OK, you may have a faulty starter motor.

Check battery terminals are clean and firmly connected.

Check the transmission neutral interlock switch operation is OK.
Check +12V is appearing on the starter solenoid control wire when the ignition switch is held in the 'start' position.

If above ok, apply +12v directly to the starter solenoid activation control -starter should immediately engage.
If it doesn't run, you likely have a faulty starter motor.

test power to starter with a voltmeter while someone else turns the key. if you are getting power, than solenoid is faulty. If you are not getting power, than relay or ignition switch is bad. Do double check your battery connections to make sure they are metal to metal contact.