My brother just gave me a hand me down EVGA GTX 570 HD Superclocked after he upgraded. It was working great in his computer with no issues. Never OC'd or anything of the sort. I have the same card (different brand) in my rig and I thought I'd give SLI a shot. For some reason when I got everything up and running my games no longer worked and would restart my computer. It always happens at the same point, right before any heavy loading occurs. You never get to the part where you actually see 3D rendering. Also my computer restarts during the windows experience test. After the computer restarts, it feels god awful sluggish, computer just doesn't feel fast anymore. As soon as I turn SLi mode off everything is fine. I'm going to take a guess that I have an inadequate power supply, but I've read that 750w is enough. Does anyone have any suggestions? Did I miss a setting? Is there something in the bios that should be changed?
Intel 3770K Ivy Bridge CPU
Asrock Z77 Extreme4
G.SKILL Ares 16GB (2 x 8GB) 1600
WD Velociraptor 600GB Sata3
Sandisk 30GB SSD Cache 30GB
Creative SB Recon3d Professional
Lite-On Blu-Ray Drive
MSI GTX 570 Twin Frozr III 1280MB
EVGA GTX 570 HD Superclocked 1280MB
OCZ ZT Series 750W 80 Plus Bronze
I'm guessing the problem is with the PSU as well. 750W is enough but personally, I don't trust OCZ's psu. I've seen lots of people complaining about them and a friend of mine even got 3 dead units after a short while.
It could be a driver issue as well. You could try uninstall the video card drivers, reboot then reinstall the latest drivers (download directly from Nvidia's website) and see if that helps.
It is most likely Amperage. I've seen this problem occur many time, and 99% of the time people only review a psu's wattage. Make sure you have a single 12v Rail @50-60amps, or 2 or more 12v rails @25-30amps. Id go with a good 60$+ Corsair, Thermaltake, Seasonic, or even Antec PSU.