Odds of 2 bad cards, very low. You did use static protection didn't you?
If not, then you could have blown the boards, admittedly unlikely, but still possible - especially in winter when the humidity is lower, and less likely to "bleed off" the static buildup.
Check for BIOS updates for your Motherboard, plug and play may not recognize the board if it came out after the BIOS (for configuration purposes). However, I'm reasonably certain that it should show up in the PCI scan that flashes by late in the boot sequence.
There can be voltage compatibility problems in the PCI bus. Older PCI boards used +5 volts, newer ones use +3.3v. (some will auto sense, and use either) There is a slot key that prevents plugging in the "wrong" board, but since it was a late breaking add-on I'm believe that it won't prevent all cases of incorrect installation. Likewise for the 66Mhz key.
I have an Intel 915GEV motherboard that appears to be operating normally. It detects some cards just fine, but not my Linksys PCI wireless network adapter.
At first I thought the Linksys card was dead, so I returned it and got a new one. Well this one doesn't work either. I've tried it in multiple PCI slots (including one that I know works for another card), and I get nothing. The card does not show up in the device manager, even when I tell it to search for new hardware. The install software won't run without the card detected.
A) is there any sort of known problem with these newer Intel boards and Linksys cards?
B) what are the odds that I got two defective cards in a row??
C) is there any sort of manual way to force this thing to work without relying on the autodetect?