any ideas on an electrical fault on 1997 ( R reg ) 1.6 scenic?

hi i have a megane scenic 1.6 petrol on a 1997 R reg that wont open the doors by the key , when i turn the ignition on it wont start , the windows wont open , the central lock buttin on the dash doesn't work nor any external lights but all the dash lights up , the sterio comes on and it turns over . i have had the key checked and checked all the fuses and there all fine , and i am completly lost what to check next .... any ideas