So today I had to take my 3DS apart because of issues with the shoulderbuttons again. When I put it all back in place and plugged it in, the screen remained black. It does however show up in my device manager under Universal Serial Bus devices.
I haven't touched any of the capture card related things aside from the flat wire that connects it to the motherboard, obviously, considering it needs to be released to be able to get to the shoulder button stuff.
Tried wiggling the cable, tried restarting the software, made sure everything was tightened and properly in place but nothing made a difference. It worked fine earlier today and any day since purchase.
Edit: As it turns out, the connector of the flatcable has a chip in it which might stop it from connecting properly? It worked fine when I tried it earlier during the day and when I opened it up, it was already chipped.
Edit 2: Angle of the photo makes it look like a pin is missing, but it's there.