I tried in Windows Media Center and also with the TBSViewer but both of them showed no signal. I even switched the card to a different slot but that didn't help.
At the moment, the card is in the PCI-e x16. Both tuners are connected to the LNB and have the same problem.

Here are some technical detail about my system:
OS: Windows 7 x64
MB: Asus Maximus Formula III
CPU: Core i7 860
RAM: 4x2Gb Mushkin
Graphics Card: Saphire HD5870
LNB: Hirschmann CS 320 T
I hope someone can help me with this issue.