I got my 2002 X5 3.0i Sport on Friday, and noticed that "Computer" from the main menu was greyed out at the time, but thought nothing off it. However things have gone downhill from there.

Things have deteriorated over the weekend, with a number of different random things happening every time the car is started :

1) Nav screen comes on, and limited options available from the main menu. Sometimes Sat nav is available, but not COMPUTER, TV or SET. Seems different each time and sometimes option available for 2-3 minutes then becomes "greyed" out. When SET is accessible, setting time or other options do not seem to be retained.
2) Nothing on screen - No response from audio or nav/TV other controls around the sat-nav screen - No matter what you press, no response and you can't turn on the radio/CD/tape, as left on/off button also dead
3) Tried to start the car and prompted for CODE, despite never enabling this. Luckily 0000 worked, otherwise I'd have been going nowhere.
4) Radio comes on, but no screen response and cannot be switched off, changed to another station or volume altered. Basically the only way to stop it is to turn off the ignition !!!

Do you think this is something as simple as a flat'ish battery, or something altogether more sinister ?

Would appreciate any advice as I need to try describe to my dealer tomorrow and would be great to know where to start !!!