Anytime I upgraded the NAV dvd version, it was a restart of the whole idrive which I accomplished by powering off the engine/computer completely. If I recall, it needed a few additional minutes too. I've never done the "soft" reset you describe to upgrade NAV (because of the additional minutes needed) though I've done it for other reasons. I've never seen a blank white screen like you describe.

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr