I have a dead internal slot.
There is some usefull info in the thread about my problem (given by others) on to see if the problem is a incorrect "doorlock" or so http://www.internettablettalk.com/fo...ad.php?t=16127
I hope it helps, I did not managed to get mine working, but ruled out some stuff...
I had the same issue and found that if the N800 is connected to a USB, you will get a "No Memory card inserted" message. If I disconnect the USB cabled from the N800 and restart File Manager, the SD cards are available.