Mihail,
I have had a multitude of issues with the new 5.1.2 Decklink drivers for windows because of the following.
When one uninstalls the old Decklink drivers they do not completely uninstall from the windows system directory. AFter installation of the new drivers Windows will detect new hardware and offer to install drivers automatically. With this choice however windows somehow finds the previous old drivers and installs those……NOT GOOD. You must instead choose to look for drivers in a specific location and point windows to C:\Program Files\Decklink or where ever you installed the Decklink executable.
Hope that this is helpful.
J