To play Nintendo 3DS games on your PC you need the emulator, and you need a 3DS BIOS, put the BIOS map inside the map with the emulator. And you will be able to open .3ds roms with the emulator.
Instructions:Step 1: Download the Bios.
Step 2: Put the Bios files in the same location as the emulator.
Step 3: The emulator will now detect the bios files.
Step 4: Done!
If the download won't unlock, Tweet, Like, Google+1 ect.. then try to download again.