GTX 670 factory overclocked possible power consumption problem?

I recently bought an ASUS Gtx 670 Direct CUII OC 2GB videocard. I installed it with the 2 6pin cables, but the card just does not want to work. There is chime, no diagnostic error, but all I see is a blank screen. I have 2 drives (1SSD, and 1 HDD) in my system.

On the SSD I have 10.8.2 Mountain Lion. When I only boot with this drive, there is nothing, keyboard does not work, occasionally reboots. Can`t select Bootcamp partition with non functioning keyboard.

On the HDD I have 10.7. With this OSX I hear the drive working, even though there is no signal and all I see is a black screen the system is up and running, because I can shut down with the keyboard shortcut.

I was wondering how to make the card work, or maybe there is something with factory over/clocking that makes the trouble? It`s on 1058Mhz on default...

I had a 8800GT before, but it just died. So I don`t have any other card with an EFI rom.

Any suggestion would be greatly appreciated!!!
Thanks in advance!
Robin

Thanks for the answers. My main boot drive is the SSD.
I was thinking about this baking, but even if it works, how am I supposed to drive 2 video cards if there's no more power source is available?

Just popped the card into a pc and it started without any hassle...
So the card is OK, just not in my Mac.
What about Mac Nvidia driver? It supposed to be integrated with Mountain Lion. But if I dont have video signal, I believe its a hardware problem. What could possibly go wrong in a Mac Mobo? SSD system wont boot, HDD Snowleopard does. WTF?

I have 2 monitors (30" and a 24") to my old 8800gt I hooked them up with DVI. With the Gtx670 I tried to connect both and only one with Dvi and Displayport in all possible variations. I tried it in Slot 1 and 2 as well.
I believe there is a problem with the main board, cause there is zero signal coming out.

Oh and the fans spin up every time.

I have the early 2008 Mac Pro 3.1
I do have another 23" monitor, but I don't know what difference it makes to change the peripheral. It either shows screen or don't depending on signal.
Or maybe if the settings are tweaked those can cause this no signal bogus?

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How do you achieve this screen sharing?

Hey Ashman, you were right!

It wasn't a hardware issue.
So in my final and last attempt I made the leap of faith and revived my 8800GT with the famous Bakin' technique...AND IT ****ING WORKS!!
I couldn't believe it, but it does. I followed a very thorough guide on youtube, and 20 something minutes later, I saw my beloved apple boot OK, it was more like 1,5 hours. I cleaned the card previously. So I only had to bake it and thermal paste it again.
So I immediately checked the firmware of my Mobo. 1.3 OK it's up to date.
I downloaded and installed the latest driver for Nvidia for 10.8.2 ML.
Changed to the GTX 670....and guess what?

It works like a charm.

So in my rare case, the driver was not included in ML.

Thanks again for everyone who tried to help me, keep on bakin' and tryin'