How do you test if a PCI slot is working - motherboard diagnostic software?

"The best way to troubleshoot a slot is with need another, known-good slot, preferably on another motherboard. Place the card in another slot, and if it works there, the first slot is bad. If it doesn't work in the known-good motherboard, it's probably a bad card.

If you have multiple cards and multiple slots on the same motherboard, trying the cards in different slots might help. Remove all cards but the one you're trying to troubleshoot, and try it in different slots in turn. Again, if it works in some slots but not in others, the card is fine, and the trouble is on the motherboard. This isn't as certain as using another motherboard to test, but can be useful if you don't have spare parts lying around."