Hmmm
My nano gets recognised with or without a card in the slot. I am using Win7.
Win7 takes ages to recognise any usb device first time, but it does find it.
Another thing you can try. Do you have a USB adaptor to lt you read the micro SD card? Might be worth trying formatting the card and adding the dat files that way.
FWIW I am usig a transcend 2GB SD card