Never changed battery before ...Is there a special way to replace it.. I was afraid there maybe some electronic reset.

It seems like you're having issues with your BMW 320d after experiencing a flat battery. Here are a few steps you can try to resolve the problem:
1. **Charge or Replace the Battery:** If the battery is completely flat, it might need to be charged or replaced. A weak battery can cause various electrical issues in the car.
2. **Reset Steering Lock:** Modern vehicles often have electronic steering locks that engage when the battery voltage drops too low. To reset this, try the following steps:
- Insert the key fob into the ignition and turn it to the "On" position (do not start the engine).
- Gently turn the steering wheel left and right while keeping the key in the "On" position.
- Attempt to start the car.
3. **Check Fuses:** A flat battery or jump-starting process can sometimes cause a blown fuse. Check the fuses related to the ignition system, starting system, and other relevant components. If you find a blown fuse, replace it with the appropriate one.
4. **Perform a Hard Reset:** Sometimes, performing a hard reset can help resolve electronic glitches. Disconnect the negative terminal of the battery, wait for about 15-20 minutes, and then reconnect it. This can help reset various electronic systems in the car.
5. **Diagnostic Scan:** If the above steps don't work, you might need to perform a diagnostic scan using specialized equipment. This will help identify any specific issues or error codes that are causing the problem.
6. **Seek Professional Help:** If none of the above solutions work, it's recommended to take your car to a BMW dealership or a qualified mechanic who has experience with BMW vehicles. They can diagnose the issue more accurately and provide a solution.
Remember that modern vehicles have complex electronic systems, and a flat battery or jump-starting process can sometimes trigger unexpected issues. It's always a good idea to consult with a professional to ensure the problem is properly diagnosed and resolved.

If the battery was flattened, the horn is sounding because the immobilizer and alarm needs resetting.

anti-theft reset

https://www.google.com/search?q=2004+toyota+solara+anti+theft+reset

The safest order to attach the jumper cables is as follows:

1. Attach one red jumper cable clamp to the positive terminal on the dead battery.
2. Attach the other end of the same cable, the second red jumper cable clamp, to the positive terminal on the working (live) car battery.
3. Attach one black jumper cable clamp to the negative terminal of the working (live) car's battery.
4. Attach the other end of that cable, the second black jumper cable clamp, to an unpainted piece of stationary metal on the car with the dead battery. Do not attach this clamp to the negative terminal on the dead car's battery.

..

The door locks are electronically operated by the key fob communicating to the ECM or BCM. The Immobilizer works by the transponder in the key communicating to the receiver near the ignition lock, and communicating to the ECM to allow all the items needed to start the vehicle.

It sounds like you just need an auto-electrician or the dealership to reprogram everything.

If its anything like a Ford, changing a sensor throws the electronics into a frenzy. Try completely disconnecting the battery and leaving the car for an hour to completely wipe or reset the electronic programs. Reconnect the battery and try the car again. The electronics should have reset to the factory standard settings and will communicate with the new sensor.

Modern cars do have electronic systems, who can lose all information, when the battery is disconnected. Special when the backup battery in the electronic system is not charging anymore. I'm afraid you need to setup the electronics again. Check your manual or visit a repair centre.

I have never heard of a car that changing the water pump requires access to the timing chain. Just the wreches.

not really this is now a dealer only job iam afraid ,encrypted software is used on the immobilisor to stop anyone from stealing the car so it will need their special diagnostic software .Sorry for not being more optomistic

Common problem - normally caused by low battery voltage. Disconnect battery for 10 mins (MAKE SURE YOU HAVE YOUR RADIO CODE) reconnect battery - then follow instructions on dashboard to reset park/brake. Use this method for all p/brake faults as 95% of the time it resets them. Hope this helps - good luck.

Make sure you are using premium gasoline and have the car scanned (OBD2) most likely you will need to replace O2 sensor.

Should be able to take it apart and take the battery out for 15-30 seconds or longer. Then put it back in. While your at it, you might as well change the battery but doing this will reset it.