What is exact BSOD? Also, you can afford two top of the line sli gpus but can't buy a multi meter tester? The only way you'll know for sure if your psu is adequate is to test the psu with multimeter, of course each amp individually. Meaning you won't get the full loop green light for all rails including input/outlet. This of course will give you more minor readings, but of course your psu is dedicated to many things, and expansion cards don't come first.
I'm not an expert with this stuff, but I'm just assuming. Could it be your board?? How many pins does the psu dedicate to the pic expansion lanes? 4? 6? Remember, heavy graphic cards fit into old pcix16 expansion slots made for sli compatibility(funny, how I call that old)
Yet that doesn't mean when the main board architecture was designed, that they knew that the gpus that would fit into Those expansion slots, and be sli compatible to run two hard core gaming gpus. Does the motherboard interface support that high of expansion bit processing?? Of course. But each slot was made for one interface card, and with that in mind they may have thought of older cards or mid line cards being made for sli compatibility
So you have a 750 watt psu. It's not bad. Not that the wattage equals the quality. Perhaps you think the watts are high and rails are low for amps? With a multi meter you'll have your answer.
Here is a good example of why it may be your board. I had a friend who recently built a gaming computer. He built one, with semi decent specs in mind. He got a board based on sandy bridge technology. I forget what socket but it supports the i3 processor. He put In a 64 bit version. 8 gigs ram, good motherboard not brand new model though. He used a 600 watt power supply, even at 600 watts it was a good brand cost him $95. Installed windows on a terabyte drive. Everything was fine.
Now here is a giveaway, he used Sata 2 instead of sata3, as said before, this board is good just not the newest. Now in a pci slot, he put the brand new nvidia graphics card, blah blah I forget what it was, the one with a 256 bit bus processor, 2 gigs ddr3 VRAM, etc. turns out his pc blue screened with the new video card. He tried every pci slot. Just didn't work. Turns out, even with the processor normally clocked, etc. good psu with good rails, his mobo didn't have a power pin interface to power that card in a pic slot. I couldn't believe it either.
And really, same issue. Pc turned on. Game didn't run, pc blue screened. He tried new drivers, etc. etc. etc. lower settings. He took it to geek squad, turns out when his gpu bench marked, and peaked, that his psu was missing about a watt or two of power to run battlefield 3, with that card anyway. I'm assuming he did ok with YouTube. He almost just replaced the card and they convinced him the gpu was more expensive then his main board. 
He got a newer mobo, re installed everything, re mounted it, I think he needed a newer heat sink made for an i7 instead of an i3. That was it and now he can run anything.
Its hard to believe that your psu isn't the issue, but its most likely not. One hard core gpu works. Prolly two older gpus would work side by Side sli connected. And of course a blue screen is any memory issue, a pc turning off is a power issue, more CPU related or total failure. A blue screen is more ram, or one motherboard interface memory issue, like a gpu issue. If you test the psu with a multi meter and it's good it's most likely a mobo issue. Meaning the designers didn't figure server type,power would e pulled from the expansion slots. It's amazing when bright engineers like intel, hp, dell, Asus, don't initiate this shit.
So you'll say, what were the chances the board interface expansions were made to pull enough bits to power latest technology, but they didnt make a power interface for all the lanes to run two sli cards. Well, engineers make an expansion slot interface to work for generations. If I made Sata 12, I might make it tomorrow, to run 100 gigs a second. Doesn't mean a processor and storage drive would be made in the next week that would fully utilise this ability, or even close
But when the power to the lanes is designed, it's designed with the idea in mind of what's bench marked at the moment. Now right now a gpu exists that has a 512 bit bus, and 4 gigs ddr3 VRAM. Tomorrow there might be a gpu that doubles that that's sli compatible, while today engineers are trying to make sure enough power goes to expansion slots to power a gig NIC, a sound card, and one 512 bit bus gpu, on the newst main board architecture. Which might be less power altogether then two gpus sli connected that each individually double the highest standard right now.
Think I'm close? Sucks counting technology in a generation, that's behind by only a few bits, or a few amps, or one watt. It's just how the market works. Today's top of the line shit will run battlefield 7 on the lowest settings
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I did not say to edit my signature soulidarity! Now forever I will never remember what I said about understanding the secrets of the universe by paying attention to subtleties!
I'm never giving you the password again. Jerk
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