Megane 03 - ticking noise, battery disconnected now dead?

Hi, can anyone help?? By car wouldn't turn over, all the dash was on and stereo, we looked at the connectores and made sure it was all working, cleared out with electrical spray - disconnected the batter for a second whilxt doing and then all the power had gone completely. thought it could be the immobilisor so disconnected battery for half an hour to reset - i can get nothing from the car now, dead, nothing - not even reconizing key card. Any ideas anyone???