Perhaps the contacts are a little dirty. Try rubbing them with an eraser or an earbud + alcohol. Other than that, you could also clean the molex connector on the top right. If that doesn't work, I suggest taking a good look at the card to see if there are any missing capacitors or SMDs, there are some very high quality photos of the V5 online that you can compare with.

If all of the above fail, you try baking the card, but the results will vary 🙁.

another idea by myself:

what AGP voltage does the card use?

I have to check of my boards can provide the correct voltage

I'll check the contacts, but I think they very clean. I have experience in cleaning them as I collect old videogames^^

Every slot1 board will be working with any voodoo so agp voltage is not your problem here.

Check all the tiny components.

You should best contact Oscar and have him have a look at it. Are you located in Europe ?

Lets hope the previous owner didn't plug it into the wrong sort of board. You could try booting with another card and this 5500 plugged in to see if it is detected at all.