Stuck at "Loading Operating System" with SLI

[Shugsogoth]

Working with a fresh scratch built computer here.  I got the system up and running with the GA-P55A-UD4P mother board, a fresh solid state hard drive, and a GeForce GTX 460 graphics card.  I installed windows 7 and after a few hitches, got the system up and running.  Loaded drivers for the various components and everything was running fine.  I then added in an old hard drive I had and again, things worked fine.  The problem came when I attempted to add in my second graphics card to set up SLI.  I am using identical graphics cards (same manufacturer and model and everything).  When both graphics cards are in the computer, the computer will post but it freezes when it gets to the "Loading Operating System..." message.  I've left it there for over 15 minutes with nothing happening.  If I remove the second graphics card, the system boots up just fine.

Things I have tried.

1) I have swapped out the 2 graphics cards, both of them work just fine individually

2) I have swapped out the power connectors going to the cards from the power supply (850w with up to 67 amps on the +12 rail), both sets work fine on the one card in the system. (note: when both cards are plugged in and powered, the fans operate on both cards, so I know they are getting power)

3) I have set the "Init Display First" option in the bios (F14) to use the second card to display though.  This works fine while in the bios and other pre OS screens but then blacks out when it gets to the "Loading Operating System" message.

4) I have tried running the cards with and without the SLI connector bridge.  Both setups have the exact same result


Any help with this issue would be very much appreciated.

[Dark Mantis]

Hi and welcome to the Gigabyte UK Forum.

Sounds unusual. Have you tried using a different bridge in case that one is faulty?

Is your PSU a single rail 12V supply?

Try clearing the CMOS completely and making sure the BIOS is up to date. Use QFlash if you need to update it. 

[JakeF150]

I assume the 8 pin connector from the PSU to the motherboard is installed correctly?  That cable is used to boost the power to the PCIe slots.

[Shugsogoth]

Cleared CMOS, and loaded the failsafe defaults but still had the same problem.

Unplugged and replugged the 8 pin motherboard cable but still had the same problem.

Used Q-Flash to go back to the default BIOS...same problem.

Downloading the latest BIOS now.  I'll post again in a moment.

[Shugsogoth]

No change, even with the new bios.

Three points of note:
1) Appears that the power supply is running on a single 12 v rail.
2) The same problem occurs even if I attempt to boot off of my windows 7 cd.
3) I have tried booting up both with and without the SLI bridge attached.  I do not have a spare bridge so I can't test that, but the system should run without it (albeit at a reduced rate since the bus will have to do the bridge work).  Correct me if I'm mistaken on this.

[Dark Mantis]

Flash your BIOS to the latest F14 BIOS version (if you have the revision 1.0 board) with QFlash and make sure that you Disable the Keep DMI Data on the QFlash homepage.

Not that I expect it to cure your problem but you should have loaded Optimised BIOS Defaults NOT Failsafe BIOS Defaults

Do you have any other cards installed ?

Have you got the EATX 12V connections attached to the motherboard ?

[Shugsogoth]

I do not have any other cards installed.  Excluding motherboard, ram, and power supply, the system has:
1) 1 SATA solid state hard drive
2) 1 SATA hard drive
3) 1 DVD-R drive
4) 2 graphics cards

The EATX 12V connections have been plugged in since the beginning.  I disconnected them and reconnected them recently just to make sure but that didn't seem to fix anything.

I will attempt the BIOS flash again with the "Keep DMI Data" disabled and see how that goes.

[Dark Mantis]

Everything points to a lack of power. I don't think you actually said what PSU you are using but in my estimation it needs to be more powerful.