Dunno if it's any help but I have had a similar problem - cards not showing up in the internal slot but working perfectly in the external one.

I have managed to get the slot working again a couple of times by removing and inserting the card several times, making sure it is really seated well, and clicking the sliding metal securing thing back into place very firmly. In any case the card won't show up as working in the internal slot until you put the back on the N800.


It is quite frustrating though, as the the internal slot will then work fine for a week or so, before spontaneously disappearing, and without (configured as virtual memory) the N800 seems to run appreciably slower.