Thanks for your reply Brian. Here is some more info on the problem.

1) My NAV system is original to the vehicle- I purchased it new when I purchased the X5 From the dealer back in 2000 - I am the original owner.

2) I do not get any sound in the car now. I used to get sound when my NAV started 'blinking". I would enter in an address int he NAV and then when it went to calculate the directions it would reset back to an empty address. This happened at first then eventually i could not get into the NAV GPS menus without the screen turning black and then coming back on again. That it what the system does now if I put the fuses back in. I should mention that when this started to happen the stereo worked fine. As time progressed I think the stereo started to cut out a you mentioned until eventually now there is no sound at all. Is there a way to get the sound back without replacing the NAV unit at the moment? Can I bypass the NAV unit so the DSP AMP will work?

3) I have had some other odd symptoms like the turn signal flashing fast even though the bulbs are fine. It flashes fast and then works normally. Also, once in a while the hazzards will flash for no reason (that only happens about twice a year).

4) My originaly battery was replaced by the dealer about 2 years ago so I think it is ok.

Finally, you said to disconnect the battery +ve and -ve cables from the battery (where is the battery in the X5???) Sorry for my ignorance but it seems to be hidden in the trunk maybe?

Thanks Brian