Hi there,
I usually have this issue when I disconnect everything from my computer when moving it from one place to the next, I don’t know if it’s the real cause of the issue, but I fix it by unplugging everything and then I open up the computer where the capture card is installed and then I pull the card out and then put the card back in as you would normally do when installing it, the computer will then show the capture card.
I hope this helps.