🔧 No power to instrument cluster + alarm acting weird after reconnecting battery

[Hamedsafaei]

Hi everyone,
I’m having a strange issue with my BMW (please add your exact model and year, e.g., E60 525i 2005).
A few days ago, my car was sitting at a body shop for some paintwork, and the mechanic had disconnected the negative battery terminal for a few days. After they reconnected the battery, the remote key fob completely stopped working — I can’t lock or unlock the car, and it doesn’t respond at all.
When I manually open the door, the car alarm immediately goes off and starts sounding. In addition, the hazard lights (4-way flashers) start blinking and keep flashing continuously, like the alarm system is activated. The alarm keeps going for about 20-30 times, then stops, and both the alarm and the flashers shut off at the same time. It’s as if the alarm system is somehow still active even after the car is opened.
Also, when I insert the key and turn the ignition on, there is absolutely no power to the instrument cluster — no lights, no gauges, no reaction at all.
Has anyone experienced a similar problem after disconnecting and reconnecting the battery? Could it be related to the immobilizer, blown fuses, or some reset procedure I should try?
Any help or suggestions would be greatly appreciated. Thank you so much!