Electrical problems Citreon C3?

I have a Citreon C3 1.6 (2002). Door wouldn't open on key fob. Open door with key, alarms sounded, silenced alarm with fob. Car started normally however, brake, airbag and other warning lights stayed on, clock and radio didn't work. Turned off engine and all warning lights stayed on after removing the key. Also electric buzzing sound. Disconnected battery and reconnected a couple of time but problem remained...nay ideas?