Re: No X display via HDMI with nvidia driver 256
You use a new xorg. Maybe that has to do with your issue?
Also, if you connect a monitor to the vga/digital port of the card and start the computer with it and then plug the hdmi device and launch nvidia-settings, do you see both attached displays there?
If yes, try to disable the vga and make the hdmi your primary x screen. This can be done runtime, i did it when i changed my monitor from vga to digital connector (the monitor has both interfaces).