Just built my first HTPC and intalled 2 PCI-E tuner cards, Hauppauge 2250 and Avermedia Duet. Media center doesn't seem to work with either of the TV Tuners. It recognizes them and tells me the signal strength for each OTA channel, but when I try to watch something I get a message "Service is unavailable" - "there is currently no TV signal detected for this channel". This is true of all channels for both tuners.
I have checked the device manager and both cards have the correct drivers. I have turned the firewall off. The same cable works perfectly with the TV.
Build is Gigabyte GA-Z68MX-UD2H-B3 motherboard, Windows 7 Ultima 64-bit OS, i5-2500. Using Intel graphics, no separate graphics card.