No footage shown on screen

[graciegraceprice]

I've set up OBS and my 3DS, connected it all up, bought all the necessary leads, and I cannot get any footage on the screen. It just shows me a blank screen.
I know you can record 3DS footage as there are so many videos of people's footage on YouTube, so I don't know what I am doing wrong. If anyone can point me in the direction of a guide that would be great!