3dscapture.com

Shouldn't be a problem.
Here's what it looks like inside: https://3dscapture.com/install_old/15.jpg

Also test different USB ports on your computer.

It is probably the soldering.
Did you install it yourself?

No, that's not a problem.

You can use any shipping service.

Either address will work.
You don't need to put the phone number on the package. It's provided because sometimes shippers will ask for a phone number.

Do you have any particularly bad examples? If you haven't already, you should change your 3DS sound from surround to stereo. Audio is passed up to Windows to do the resampling, it isn't done by the capture software. I tried using WASAPI instead, you can give it a try. I'd be surprised if there's any...

Hmm. Sounds like you've done all the troubleshooting steps I would have recommended. You could try connecting it to a different computer and see what happens.
I'll take a look at it if you want to send it in.

It could be any of that. Cables not connected right, or bad soldering can make it fail to boot.
Send it in if you want, I'll take a look at it.

No.