Okay, so I am going to try and make this short and sweet
(edit: I failed). Sunday I was running 2x5850's and mining just fine and dandy...
I went to put in another 5850 that I had just purchased, and I ran into a little bit of a problem with the motherboard design. It has 5 PCI-E slots, but the power button and the SATA connection are very inconveniently located, so I had to use a riser even though I didn’t want to. Anyways, I had the riser so no big deal, rigged the 3rd card with some twist ties and rubber bands and cardboard to fit on the outside of the case. Powered it up, all three cards are spinning.
Next, I figured Windows 7 was going to punch me in the face for adding another video card, and it did, but then I reinstalled Catalyst 13.1 and Windows decided that it liked all three cards and everything seemed to be running fine.
Then I tried my normal pool, Middlecoin, and cgminer would start up, freeze my computer, and then blue screen stop error (see similar image here:
http://images.anandtech.com/reviews/system/2008/ibuypower-3waysli/bluescreen.jpg)
I fiddled with it a little more, and still got the same results with Middlecoin…
Now this is where it gets interesting. After a restart, I try a different pool, an old FTC batch file that I had, and it starts up fine. Sees all three cards, but only two of them are mining. The 3rd one is showing like 1200rpms, 0 hashes, and no other reliable figures.
Decided to swap out the 2nd and 3rd cards, and got the same results. Swapped out the PCI-E riser cable and still got the same results. Then finally I decided to call it a night and remove the 3rd card.
Now, I tried to start up Middlecoin again, and it still freezes the computer and crashes.
So I was mining my primary pool with 2x5850s, and a few hours later not only did I fail to upgrade to mine my primary with 3x5850s, but I am now just mining my secondary with 2x5850s because I can’t get anything else to work.
FML
TL;DR
/end rant