(If only computers were as reliable as Boogies)
It does sound unlikely to be two bad cards that you know work. Like GherkinPaul says, try another system, just to lay to rest that it's not the card.
What motherboard do you have?
There was one PCI slot that I didn't try because a firewire cable was being passed through that slot's blanking plate. I removed the cable and put my soundcard in that slot and windows detected it!
My mobo is an intel D945GNT that was replaced by intel after I fried my original board (see the thread DEAD PC). My board, therefore, is probably a refurb. I emailed intel, so they may be able to tell me the history of my mobo. In the meantime, no more PCI cards.
Thanks very much for your help.
Now I'm ready to install my firewire recording card and record my F-50 into a 2x12 recto cab. I hope my neighbor isn't home.