[plz4mr]

Any tips for trouble shooting would be greatly appreciated.
Last night I plugged in a brand new FM/Bluetooth adapter to the lighter socket. Then I went to start the car.
The car wouldnt start, cabin lights flickered. I unplugged the FM/Bluetooth thing and still nothing.
I checked the lighter fuse, the ignition fuse, the immobilizer fuse and several others - all were OK.
The car won't start and I can't think of what to do next.
The lights, door locks and radio work.
The top does not - however I was able to put it down immediately before trying to start the car originally.

Could this be a battery issue?
Or?

Any ideas or past experience is welcome.