Recently I was interested in moving some music from my computer onto my New 3DS XL to listen to with '3DS Sound'. I'd done this before with my older 3DS and knew I just had to copy/paste the mp3s onto the SD card. Now, this was the first time I've tried to do this with the New 3DS XL and a microSD, but I had a microSD adapter for my computer so I figured it shouldn't be a problem. I should also note that the microSD in question is a 16GB Nexxtech and has worked with no problems whatsoever since making the transfer from the pre-packaged microSD that came with the Monster Hunter 4 3DS bundle.
I turned off my 3DS XL and removed the microSD. Put the microSD into the adapter, and plugged the adapter into a USB on my computer. My computer informs me that in order to interact with any data on the microSD, it needs to be formatted first. I said nuts to that, because formatting it would obviously wipe all my games and save data. Whatever. I can live without the music. I used the 'Safely Remove Hardware' tab on the taskbar to remove the adapter, removed the microSD, re-inserted it into my New 3DS XL and powered it on.
"Could not detect a microSD Card. The software on the microSD Card could not be displayed."
Hm. Well, perhaps I smudged a connector or something. Turned off the 3DS, removed microSD, gently wiped the connectors with a lens cleaning cloth, and tried again. Same message. Put the microSD back into the computer using the same method, and it still tried to get a format done. Tried a fresh microSD card in the system, and it was read and had new Home menu data created as a fresh card should. As far as I can tell, the act of trying to open the microSD on my computer has just bricked it somehow. Help, please?