Code D6 may indicate that the board was unable to find the graphics cards for console output.
 
Are you running default BIOS configuration? If not, have you done any bclk adjustments? Sometimes too great of a bclk increase can cause the graphic cards to go offline. You might also try and update the BIOS to the latest version.
 
If BIOS is default, then try airing out the PCI-E slots and reseating the graphics cards. If that does not help, pull the processor out and check for any bent pins in the socket or debris present in either the socket or on the processor contacts. The PCI-E controller is integrated with the processor and there may be poor connectivity with one or more pins.
 
Also, make sure your PSU is able to provide sufficient power to your graphics cards.

I remove the vga card and reseat the cpu and change the memory for kingston beast and it work great now . thank for your help.