Unable to configure a Triple monitor setup

Apologies if I am in the incorrect location for this post, i have what seems to be a simple problem, according to some of the articles I have read over the last week or so, although I'm unable to resolve it, I am just attempting to add another monitor to my set up?
My current rig as as follows:
3.40 gigahertz Intel Core i5-3570K
ASUSTeK COMPUTER INC. P8Z77-V LX2 Rev X.0x
8142 Megabytes Usable Installed Memory
NVIDIA GeForce GTX 650 Ti [Display adapter] (2 DVI outlets and 1 mini HDMI outlet)
the 2 monitors I have running at the moment are a Samsung S24B150 (No2) and an Acer S240HL,(No1) both with resolutions of 1920 x 1080, and using both the DVI connections
TheGeForce GTX 650 Ti has sufficient capacity to connect another Screen but when I connect the additional screen existing screens go black and No1 actually turns off.
Please let me know if any further info is needed to locate the problem.
Thanks
Jim

I would try disconnecting the main two monitors, plug the new one in and try to boot up using only your new mini-hdmi connected monitor. Make sure that works. If so, power down then add back in one of the other two monitors, boot up again. If not, try the monitor on another computer.

btw anytime you are windows you can do start > run > rundll32.exe shell32.dll,Control_RunDLL desk.cpl > detect to find out how many monitors windows "sees"

Make sure your 6-pin power cord is plugged into the video card. Since you have two monitors working already I'm sure it is, but just want to mention it

Thanks for your quick response.
Connecting the single Monitor doesn't work, sorry , should have mentioned that, trouble is I've tried so many things? I've just this minute been reading about the power connection, will try this later this morning, it seems like a power problem doesn't what with the monitor closing down like that, maybe I need to review the power unit capacity of the PC.
Thanks so far, will come back to you shortly, I hope!
Jim

Hi, not sure why but I have success? I carried the connection and re connection as you suggested, bearing in mind I had done this on a number of previous occasions....Put the kit back together again last night and Hey Presto, all is up and running.
As I said I don't know why, perhaps you cast a spell on the internet or something, anyway thanks for your advice, and apologies for any inconvenience,
Best Regards
Jim

i think you need a 660 or above.... does your nvidia control panel have the option to "span displays in surround"? if so it might be ok.

also....the dvi - i and dvi - d sockets are different. if possible dont use the dvi-d socket as this will mess up and try to output an analogue signal instead of a digital one like out of your dvi-i socket and hdmi socket.

Thanks, but the problem seems to have resolved itself? don't know how or why