Attached Link: SLI Zone Forums

As long as your monitor is connected to #1 card either spot your good to go. #1 card is the card in the #1 PCIe slot. When SLI isn't enabled you can run 4 monitors if you wanted too. When SLI is enabled windows will only see one monitor. Okay the 650i is good, I run the 680i here. Next thing is the motherboard drivers, wonder if the guys that built you system updated to the newest ones.

Now this I don't recommend you doing unless you've done it before and are comfortable
with doing it, flashing the bios on the MB. All the MB makers update the Bios when problems
are ironed out. I started with Bios26, and am with 30 now. BUT AGAIN I DO NOT RECOMMEND
YOU DO THIS IF YOU NEVER HAVE! You can render your MB to nothing more than a paper
weight.

You might want to go to nvidias forums and ask there, might be an easy solution. see attached
link. 8-)

UPDATE: Just saw that the 650i chipset dosen't support  x16 when in SLI reverts to x8, might be
what your experiencing. I know you didn't want to hear that sorry 8-(