WinTV HVR 2250 PCIe - computer won't even post

My HP Pavilion runs great under either XP or Vista (I switch system harddrives for various tasks).

But when I install my new Hauppauge WinTV HVR 2250 card in the single PCI-e slot, the computer will not do ANYTHING when powered up. No post, no beeps. The fans run and I hear the harddrives power up, but nothing else. Monitor remains black. Under either Vista or XP.

When I remove the 2250, everything runs great.

Thinking that the 2250 board was faulty, I exchanged it at the dealer for an identical replacement.

This computer has run perfectly for a year, but how can I tell if there's something wrong with the PCI-e slot?

I bought a PCI POST DIAGNOSTICS TEST CARD (StarTech) which slides into a plain PCI slot. When I attempt to boot with the 2250 installed, the test card reads 00 and nothing else.

Any ideas?

Thanks