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 etc... then try to download again.