MSI 7900 GTO 512mb

does windows load? (can you hear the da da da da of windows starting up), or is it just getting to Bios and stopping.

Which PSU there are several 550W antecs. most would be ok, but one of them, the true power, delivers 30A max on 12V, so this could be a problem?

I'm assuming you have the bridge connector in place.

Right well i dont get the da da da of windows loading, is just powers on and thats it, all fans and lights run but no sound, so i can only assume it gets ito the bios and thats it but i dont know, now the power suppy is the antec true power 550W. yes brdige etc.. is all in place, so i didnt know if it was a PSU problem or not, i was just puzzled as the fact it gives a "no signal" error like the connection between monitor and pc isnt there though all cables are tightly connected.
now you mention about the 12v supplying on 30A, how much should it be for an Sli set up? and which PSU is best? as i have the Antec p180 case and have heard if not Antec there can be problems installing them.

Also running a P180 case with a seasonic S12-600W, no problem just needed ATX extension cables.

If the card is not powering up due to lack of power it would be the same to the monitor as no signal perhaps. My old 6600GT would run at low power if no additional power was connected, new ones might not.

Single card recommends 22A (according to the box) this is really for system + card, but if a 30amp is to be enough for SLI then the card itself can only by 8A which leaves the rest of the system running at 22-8=14A. This seems a bit high to me, don't know the real figures but I'd put the 'system' at 10A and therefore each card at 12A meaning 34A Total, or if system was 12 then 32A total, either way you may be very close to the edge if not beyond with that PSU.

Have you tried the output from your 'secondary' card, I ask because I got something like this when I tried out the latest drivers 93.71 having gone back to 91.47 the video is outputted from 'primary' card, failing that check your PSU and it's supply to those cards as they do like a bit of juice and unlike my little GT's will whinge if they do not get enough.

It sounds like they are pre-driver, i.e. not even getting to Bios screens. How exact do the bios's for the cards have to be? would a minor bios revision cause this problem?

I'm sli'ing, so Ive just about run out of ides pending the power on being the issue.

When I tried the new drivers I did all the usual uninstall, go into \sytem32 folder delete Nvidia files etc, but upon reboot after new driver installation I just had a black screen and the 'no signal' message, the mobo was doing it's thing and beeped 'normal' the LED readout indicated 'FF' which is normal and as I have the sounds switched off I was scratching my head for a sec (still pulling out the splinters   ) then I tried the moving the monitors D-sub to the other outputs and and found that lo and behold my 'secondary' card had become my primary output!

As to whether the BIOS's have to be an exact match I don't think it matters as long as they are both GTO's or GTX's or as in my case GT's, mine are different brands, different core speeds and different RAM speeds and yet they play very nicely together 8) , hopefully the OP will get back to us and give a progress update.

i have indeed tried all the outputs from the cards and none work, unless im needing to update the bios and drivers, but the cards are identical bought 2 of the same type. now i did come across a bit on MSI website about if in SLi mode a 550w PSU is recommended.. so i may very well be at the limit of it.
i was wodnering if i disconnected all the other drives, dvd etc.. and see if it worked then with the extra power from those :S

Its certainly worth a try pulling everything else from the system, but it might only gain you 1-2A running load, and 2-4A startup?

If you are having that as trouble, you could get one of those 5 1/4 bay Supplementary PSU's that are specically for GPU's use one of them on one of the cards and the PSU on the other? Or run both from it, it might be a cheaper upgrade, and would come in handy in the post 8xxx world.

http://www.scan.co.uk/Products/ProductInfo.asp?WebProdu...

Can I clarify, this is happening during boot, i.e. at Bios level and not windows level.

Make sure you're enabling SLI mode correctly. On many motherboards, aside from just the SLI dongle, there are a few switched you need to change from "normal" to SLI. There could be a jumper or such that you need to change too, be sure to triple check with your MB manual.

Right well i'm still having problems getting the Sli to run, i had no luck with the 550w PSU so thought id get a new one to see if the lack of power was the problem, seems not. as i have just got a OCZ gamexsteam 700w PSU. i also checked the slizone website about PSU and what was recommended for a 7900gtx which is 650+ watts

now after installing the PSU and then putting the second graphics card in, it does the same as before really, all lights, motherboard goes through the checks on LED, but what it does is when connected to the montior it will say no signal at times, but suddenly the ABIt logo will appear for a second then will go again and give the no signal message and reappear about 5-10 secs later.
now ive combed the manual and i cant find anything about jumpers or options for putitng it into SLi mode, anyone else got any ideas as to what could be wrong ?