lantrich :
When Windows loads very slow it may indicate that there is a video problem. Is the resolution of the desktop really low? Does the Device Manager recognize the cards? When you loaded the drivers did the program recognize the cards? I would start by starting windows with one card and then the other to see if windows works properly with each card properly. It could be that one of the cards is defective. It could also be that your cards are not compatible. You didn't really explain your problem in much detail.
Okay, ill go in deep.
I have 2 GTX 660 TI cards, they have been working for at least 1 and a half year now
so, last 2 times i have enabled SLI ( i dont do this often but i have tested it and it does this every time) When i press apply, to enable SLI, the little applying changes box comes up, the screen goes black (which also happened when it worked cause after some seconds i would have my desktop again) but the screen stays black, the pc doesn't turn off or anything, there is just no display output coming from the cards.
so i restart my pc
my 2nd monitor lights up and i open my pc as normal, though on a smaller monitor, everything is laggy, like 10 sec input delay , right click barely works.
i slowly make my way to control panel > device manager > display adapters
i know see that both cards have been disabled, showed by the little grey down arrow and i can press activate on the top, doing this (pressing activate or enable) with both cards and restarting (as im asked for it to take effect)
my pc now boots as normal, and when i get to my desktop Nvidia control panel notifies me that SLI changes have been made, i go check, and SLI is now enabled.
So, things that needs fixing
getting a signal instead of nothing at all when trying to enable SLI
Not having to boot, manually activate both cards and reboot, to get cards back online
SLI just changing in like 20 sec, like it used to
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