So I built a rig using:
AsRock H81 Pro BTC R2.0 motherboard
Corsair HX1200i power supply
Kingston Value RAM 4gb, 1600mhz pc3-12800 DDR3 (2 of these)
EVGA GTX1070Ti SC (4 of these)
EVGA GTX1070Ti FTW2 (2 of these)
Silicon Power 60GB SSD S55
 
I'm a bit of a newbie when it comes to building mining rigs, but I can't for the life of me figure out why this system won't work.  When using onboard video everything is good to go...Then when I plug in the first GPU it crashes during installation every time(most of the time locking up at startup after restart as well).  I've uninstalled the cards, replaced the powered riser(twice), reinstalled Windows 10, installed the newest version of Windows 10, and talked to Nvidia support last night for over an hour.  I switched out the SC for the FTW2(which has two power inputs) and it fired up.  Then I tried to hook up two of the SC cards and it crashed again...and now it won't even boot as it locks up at the Windows screen and that little spinning thing under the Win icon is frozen.  I had no real trouble booting to BIOS, and told BIOS to search for an update but it didn't find one.  
 
Any thoughts on what the problem might be?  I'm not sure I can go any further with this, given my level of knowledge.  I figured I'd post on here and see if anyone had any ideas before I just take the computer to someone to fix or just sell the components off.  Thanks in advance for any help.

Try with 1 card. Once you get everything i stalled and working, test each card individually to verify they all work. You may have 1 bad card. Yes, it takes time, but at least you can fine out where the issue is occurring.

Once you have tested every card, 1 by 1, then start installing them until you get an error testing each step of the way.

Also, this thread would be best suited for the crypto currency forum, as thy have more experience with mining in there. They may be able to provide much better information than most general users. The mods can move it for you, so do not repost.

krashbandit
I switched out the SC for the FTW2(which has two power inputs) and it fired up.  Then I tried to hook up two of the SC cards and it crashed again.

So the FTW2's work fine, but the SC's don't? That's odd. Do the SC's work fine in another pc?
 
 
Moving thread to the cryptocurrency subsection.

Had a build I was working on earlier this week using the H81 Rev 2 - and it DOES in fact work with the GTX 1070 ti but turned out that the guy I was building it for had gotten a bad BATCH of risers - worked fine with a riser I borrowed from one of my own rigs or with a card in the 16-bit slot directly, but would not work at ALL with any of his risers.
 
 All of the GPUs were the EVGA SC model.