*If you open file manager you can format the card, if you are not doing anything special I would format it FAT32, that way it will show up on computers when you connect via USB*
*Not sure about this, I've never had it happen to me*
* are you doing anything funky like booting off your internal card?*
*In the past I have had one or both of the cards not show up when I have connected via USB but this has always sorted itself out if I reconnected.