Im sure this is a common problem but I feel like I searched everywhere and found no solution as of yet. Im a total amateur PC builder and this problem is baffling me.
I decided to upgrade my old Palit GTS 450 to a pair of Sapphire Radeon HD 6870 cards in crossfire. My method of installation may not be considered conventional but I figured it would still work, I took out the old Palit and put in my 2 new cards in crossfire before sorting any of the drivers out with the plan of using the onboard graphics during the change over. I now regret cutting a corner as it seems this may have been the start of my problem.
Basically now I cant get a picture on my screen at all, there is no power to any of the rear USB ports and It seems like none of the installed PCI cards are getting any power as well. Strangely, all of my fans are turning on; CPU, Graphics, the lot. I just cant seem to get power to the back of the board. I do have both the 24-pin and 4-pin in (im using the full 8-pin).
Im currently trying just about any solution I can find with a basic set up of simply my HDD and DVD drive attached to my MoBo.
Things I have done
checked my memory (RAM) is seated correctly
tried to startup with only one stick of RAM (in the first slot)
reset CMOS, removed BIOS battery
changed my PSU (750w)
Im fairly sure my MoBo isnt shorting against the case since its worked without issue for over a year with my old graphics card
MoBo: Asus M4A88T-V EVO/USB3
CPU: AMD Phenom2 X4 955 Black (with no O/C)
PSU: Antec HCP-750
GFX: Sapphire Radeon HD 6870 (x2)
More about :pci card rear usb graphics output power
Okay this may sound tedious, but try one 6870 card on all the PCI-E slots (turn of computer, install one card, turn on computer, to test, then repeat on other PCI-E slots) to make sure your pci-e slots didn't fry or short out. Then if it is working, you can then put in the 6870 cards and update the drivers. If the 6870's do not work, try your older graphics card.