SATNAV unit problems - Help
 

I've a 2001 bmw 5 series, E39 model with mk4 nav unit/tv. It has the latest firmware v30 and uses new bmw high 2008-1 DVD map disk. However i'm getting a number of problems in that i'm unable to adjust the units brightness from the 'set' menu; well i can but it defaults back to mid settings when i turn off the engine, but time, date etc are ok. I also find the radio sometimes stops working and takes an on/off to fix it, and finally, occasionally the tv picture goes for a split second, and does it continuously every 8 secs. I've tried downgrading the firmware and using old DVD maps and even reset the 'perspective' map view back to off but no difference.

I'm at a loss now to fix the problems. Is there a way to reset the unit to factory defaults which may fix it, and if so how. I thought updating the firmware may do that but on reboot the time, date, split screen settings are all retained so i know that doesn't reset the unit. Any ideas please people?