My BMW doesn't start

Hello.

I have a BMW 530d, 2000, 265.000 km, automatic. If I go with it somewhere and I use it for 20 minutes in the traffic and then I stop it, and I let it for 15-20 - 1h period of time, it won't start. The mechanic changed: the fuel injector, the pomp of fuel, the water cooler system and it's still acting the same. I leave it everyday in other parts of the city coz it just doesn't want to start. If I leave it for 4-5 hours, then it starts, otherwise, no chance. Any idea what the problem might be? If they test it with the machine, everything is in order.

problems which occurred from time to time:
- sometimes the alarm is not working
- one of the 5 injectors works at 40%
- sometimes the key is not working at all, it doesn't open the car, is dead
- sometimes the air conditioning is not working and it heats the car instead of cooling it
- sometimes it doesn't heat it at all but only cools it

Does anyone know what the problem might be? My mechanic is confused too :-(

Thank you,
Gina