Because this may be useful for some other user i post the problem description and solution below.
The problem was power supply. I have a BeQuiet BQ-L8 700W PSU. It has two separate cables for powering PCI-E devices. Each of those two cables is splitted into two plugs. I connected those two plugs of one cable into both power supply sockets of my GPU. But it seems that my BeQuiet PSU has some kind of power/current/amperage limitation for each PCI-E wire. When the GPU chipset was launched (i mean all the stuff that is used for 3D acceleration, not the basic VGA circuits) along with Windows (at the end of displaying splash screen) it consumed more power that a single PCI-E wire from my PSU could handle and some kind of fuse was swithing off the power for that cable. Now i connected two separate PCI-E power cables to my Pro Duo GPU and everything works fine.