help me out. P6T7 Supercomputer w/win7 only boots w/4 GPUs

[ocmoho]

So here goes,
I have 7 MSI 6850's that i am mining with, scrypt, windows 7 64 bit 12GB of ram.
Xeon W3520, powered PCIE risers.
heres how I went:
fresh win install( Win seen all 7 6850s as unknown graphics adapter>install mobo drivers>install SDK& Catalyst 12.8> then windows wont boot with more than 4 GPUs attached, it freezes on the Windows logo, the second i disconnect all but 4 it boots fine.
anybody have this problem? Im thinking of trying out ubuntu, if I cant fix this, but havent worked in linux for a long time.

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[MashRinx]

What's the motherboard model?  What power supplies (I would imagine there is more than one?) powering the GPUs?  I don't recall seeing ANY thread where anyone has gotten more than 6 GPUs working in Windows 7 (and the one thread I recall is was quite a challenge), but I may be mistaken.  I am pretty sure I have seen linux miners with up to 8 cards in a single machine, but I am not one of those miners and won't be much help in that case.

[ocmoho]

its an asus P6T7 WS Supercomputer.
two psus are an OCZ 860W as well as a coolermaster 750w.
even six i would be happy. I can get my hands on win8 if that matters, or makes it easier.

[MashRinx]

No, I don't think Win  8 will gain you anything at all.  I installed Win 8 for a little while on my primary machine (several weeks) to try to give it a fair look, but I'm back on Win 7 now.  The whole tile, no start button thing on a normal KB/Mouse machine just didn't work for me.  maybe Windows Blue will be an improvement, but I will be waiting quite a while to test that theory after release.


The only experience I had with multiiple PSU on a single mining machine wasn't a good one, but I admit I bought crap PSUs to try it too.  There are some threads, probably old, on the best way to combine multiple PSUs because of issues if you don't tie them together, and I'd point you to them if I know where to find them, but it's bee n a really long time since I've seen those.

When you are trying the 4th GPU?  Is that still on the 850, hoping to save the 750 for the last 3 (or 2) cards?  I'm pretty sure an 850 PSU is not going to push 4 cards well, regardless of the model, when given the other components also hanging off of that PSU.