2001 Citroen Xantia interior electrical faults

when I bought the car the engine imobiliser buzzer sounded continuously for about 20 secs each time I started the car and citroen suggested i live with it, then occasionally when parked the flashers would all come on for a few secs and the car would unlock (making me think I had lost my marbles and not locked the car, until i witnessed it ) then soon afterwards i have no instruments no horn no front windows no central lockin no radio no clock. Car drives well but when operate indicators instruments do mercedes wiper movements and clock flashes on in time to indicators which don't sound as they should. I've checked fuses all ok and ground terminals near battery all ok. Any ideas