Alright, I have a GA-2CEWH that I've been using for years to great avail.
I just got another 7800gt so I can have more than two monitors, but I'm having problems:
Both graphics cards work, both pci-e slots work; when I have pci-e slot 1 with a card, then pci-e slot 2 doesn't work - when I have pci-e slot 2 with a card and no card in pci-e slot 1, then it works. But when both cards are installed only the one in the first pci-e slot works...
I've ruled out power, I've tried with and without the bridge, I've enabled and set to "auto" both pci-e slots in the bios. This is not a driver or OS problem; the screens get no signal in my case.
The only thing left I can figure is a bios update - I have version F10, but I haven't seen anywhere that the GA-2CEWH needs a bios update for SLI (which many people have done successfully).
Well it is a PC Power and Cooling PSU - with two outputs for pci-e 6pin - and both cards actually work and start without the 6pin connectors, but the screen only shows no output in the instance I described.
Unless the 2nd PCI-e slot only doesn't get enough power when there is something in the first slot, then I don't even think that would be a 'power problem'.
Here's the problem I'm looking for, so you don't think I'm just trying to annoy you: many power supplies have multiple five volt 'rails', and, although the overall spec for the PSU look sufficient, often both GPU plugs come off the same rail, and sometimes can't support the current drawn by both cards...
you can try to disable all devices you don't need in bios-advanced and in bios-advanced-pci configuration disable option rom scan for pci and pci-x slots you don't use also disable pci-e x1 to free some bios rom spacem. if no go play with enable/auto for pci-e x16.
that is one good ps, mfg. say min 450w for sli. maybe you can also unplug some hd's if you have a lot of them just to try to boot or power second card with external ps if you have one.
maybe there is bios update for your video card.
i did update my bios to f14 without any problems it is easy to do and you can always go back to f10 if you don't like it for some reason(there is less memory config, i can live without), at this point you got nothing to loose.
Oh, so you have the same board and you can do SLI (or just more than two screens)?
I think I ruled out lack of power before with some weird switcharoo acrobatics, but I don't remember exactly anymore (I'm just sure it isn't a power problem after calling PCP&C and ruling stuff out). I'll check out updating the bios of the video card, but that was not suggest when I called their tech support. I'll also check out the bios update for the motherboard. But yeah - there really isn't anything else it could be is there (besides broken hardware)?
Why try disabling all these devices in bios? I think I've tried some of it before, and I disable most of what I don't use - but maybe you have a different intent. I definitely messed with the auto/enable/disable pci-e for a while with no change in operational behavior.