I installed today a new Radeon hd 6850 in my computer. With the 12V power connected from the main power switch (6pin 3 yellow/3 black), the computer does not start up - with the connector disconnected, the computer starts normaly, but the card is not found in the hardware. The mainboard is a Z68X-UD3H-B3 from Gigabyte with i5 2500K processor and 8Gb Mem.
No signal from the card when connected to the monitor. The graphics cooler on the Radeon card works normal.
What can I do?