Hi...I have just build a system MB is gigabyte GA-870A-UD3, 4 gig DDR3 1333, Athlon II quad core,and graphic is pci ex x16..the problem is it will not POST. the manaul instructs to connect the 24pin power and the 8 pin 12v but it wont power up with the 8 pin 12v connected either way no POST..any ideas?