X5 won't start (no power)

[Kingfisher]

I was trying to install new tail lights today, then there was beeping sound came from the front of the car(I guess I triggered the alarm?) it lasted for like 5 mins or so, I kinda ignored it and keep installing my new tail lights. When I was done with the tail lights and try to start the car nothing happens when I turned the key, no dash lights except airbag light, no cranking, no interior lights, I thought it was the battery(battery was fully charged yesterday) so I took it out and it was still fully charged when I hooked it up to the charger.
So maybe it was the alarm went off and completely cut off the power?
Any ideas would be much appreciated!