I have 2 GTX 780ti cards. I changed a setting in Asus GPU Tweak for Target Refresh Rate. The screen went blank.

I reset the computer and it displayed the bios and Windows loading screen OK, but the moment the Welcome screen comes on the screen goes blank (without displaying the Welcome screen). The problem persists into Windows.

I changed the monitor to the second DVI output on the top card and it displayed OK. To isolate whether this was a software problem (GPU Tweak), I removed GPU Tweak from the computer via Uninstall and returned the output to the top output. Same problem.

I then swapped cards by swapping the cards positions in the case to isolate whether there was a hardware problem with the top card's top DVI output. Same problem, the second card will not display when connected to the top output, but will display fine when connected to the second output.

Help!

This is a really mystifying problem. Although the cards my work fine when the display is connected to the second output, I don't really see this as a fix so much as a workaround. My understanding is that there is a small performance advantage when using the topmost output. Even if there is no advantage, I would like to sort this problem out if possible. What I think is happening is that somewhere I have changed a setting in Windows or Nvidia Control Panel that states that the top output must output at a Refresh Rate beyond the capability of my monitor, but I'll be stuffed if I can find where.

Thanks in advance to anyone who can help.