My expirence in fitting alarms, they have 2/3 inline fuses trace back from the siren in the engine bay (the main box will prob be driver passenger footwell plastics) and make sure there not blown because if they are and the installer has imobilised some if the ignition wires could stop radio and windows from working sounds to me like alarm related. if its fucked the alarm all you need to do is find the ign sence wire from the alarm ( that meen the wire goes live when the ign is on and stays on while cranking) and cut it and the car will start.