Satnav has removed itself!!

[Silverback mike]

What's that all about then folks? The satnav has binned itself. Doesn't even register on the home screen now!!! How do I re install that then? I think I've got the disc...

[CondorX5]

You could try resetting everything by disconnecting the battery and reconnecting -that resets the cars electronics, which seem to get in a right tizz as they get older!   
However,  I had no less than three replacement MKIV Satnavs under warranty at crazy prices (luckily not to me) as they did similar things - they do sadly just go faulty, I think the laser from memory, is the culprit. There are repair services online for them, or you can try a breakers or ebay or even sometimes on here, replacements are about £40-£60 used, obvously a risk they are knackered or will be soon.  New prices are so mad no-one would consider them (over £1500) as the satnav is very dated and not even as useful as a Garmin or a TomTom.
Luckily the satnav unit is easy to access and replacement does NOT need coding to the car, unlike the E70 and upwards.

[Silverback mike]

Well....it came back but fails again after about 5 mins and jams. Not too worried as the phone and stereo works. I'll just get a tom tom and slap it on the windscreen I think!

[X5Sport]

The Mk4 system is a bit limited in what it can do and a modern screen mounted one will very likely offer more.  I use a Garmin in mine, mainly for the DAB based traffic system which is updated at 30 sec intervals instead of the 30-mins that TMC can provide.  That and the map updates are free!