2xGPUs=No Windows Bootup.Is it my PSU?

NFL_Psycho

NFL_Psycho

NFL_Psycho

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I've just got a 2nd BFG 7800 GTX OC 256 to sli.Without this 2nd GPU installed my machine runs fine...boots up and runs windows no probs. But when I install the 2nd GPU the MB bios runs but then windows fails to run so it goes to the screen stating windows failed to run, then you can select to run safe mode etc. What I thinking is that my PSU just doesn't have the power. The PSU is an OCZ Modstream 520W. I thought that 520W would be fine when upgrading to sli but I guess not. Is it the PSU thats causing my sli to not work (ie the amp on the 12V)?
 
Seems a bit surprising, I too would have thought that the OCZ 520W would be enough. Have you tested each of the two cards seperately? If you think it might be the power supply have you tried removing anything that isn't required from the system, like extra optical drives?

When you try each card seperately see if the cards have the same BIOS version - not sure if it would cause your problem, but they're supposed to be the same for SLI to work properly I think.
 
I've tried the cards seperately (both BFG 7800GTX OC) and they both work fine. Both have the same BIOS too. The other hardware using power from PSU are Sound Blaster X-Fi Fatal1ty, Gatewatch Aerocool with 4fans, 4xUV Cathodes (turned them off), A8N-Sli Premium with 3fans, 4x1GB OCZ DDR, and 2xdvd drives.Tried both GPUs with UV cathodes of, Gatewatch n 4xfans off, n 1DVD drive off. Same result as before tho. I think it maybe a lack of Amps on the 12v line. Looks like BFG recommend 12V with rating of 34A or more n I think the OCZ 520W has 12V rating of 28A.
 
are you sure the 'switch card' on the mainboard is selected for sli and secured properly ? or does this mainboard use the bios to select sli mode? I heard of a similar problem to this in which the bios was set for single/non sli mode, but the user had the cards joined together on the outer edge of the cards with that ...........ya know the thing that you join the cards with, sli bridge cable thingy, sorry carnt think what its called ! :D, anyways it didnt work properly until the board was either set for sli or the sli bridge was removed and the cards worked as two seperate entities
 
It does sounds like power issue to me although that PSU should be able to cope easily. You could try disconnecting any unnecessary components (e.g. extra hard drives, any memory above one stick) and see if it helps. At least it may show where the problem lies.

You could also try running them in non-SLI mode as two seperate gfx cards to see if it's an SLI driver issue.
 
NFL_Psycho said:
The PSU is an OCZ Modstream 520W. I thought that 520W would be fine when upgrading to sli but I guess not. Is it the PSU thats causing my sli to not work (ie the amp on the 12V)?
Click to expand...

Could be a possibility, in the spec on the BFG cards is states minimum of 500w for sli'd cards.
 
Messed around this morning trying variuos ideas. As it stands both GPUs are installed with their fans a whirling so theyre getting power. Set the ASUS A8N-SLi Premium Bios to Dual graphics setting, fitted the bridge and windows failed to run so up came the message that windows failed to run, select safe mode etc. So I then changed the Bios to single graphics card setting (left the 2nd GPU installed) and windows booted up fine with no probs. 2nd GPU is getting power as fan runs. Just windows wont boot when bios set to dual graphics cards and both card are installed. Anyone had similar problems? Could it be the MB or just a lack of Power for the 2nd GPU unit to actually run?
 
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