-m4a785-m pro motherboard
-AMD Phenom 4 core Processor
-modecom Premium 500w PSU
I just pluged card to pcie slot.
So, you didn't connect a chord to the 6-pin power connector on the card? If not, that's your problem.
You MUST hook that up as the card requires the extra power to operate.
This picture shows the connector in the lower right-hand corner: