I'm guessing you installed that new 10.10.1 Yosemite update. So you'll need this driver.
http://www.nvidia.com/download/driverResults.aspx/80070/en-us
Boot using -x and remove the NVIDIA driver you've currently installed. Download the driver above and install which I think will force a reboot. Boot using the nv_disable=1 and open the NVIDIA device settings and select the NVIDIA driver. Reboot again (you may have to retry the nv_disable=1 process again at this point) and then that 3rd time you boot your video card should be working.
Ensure the following lines below are added in org.chameleon.Boot.plist - located in the Extra folder on the root of the drive.
<key>Kernel Flags</key>
<string>kext-dev-mode=1 nvda_drv=1</string>
All 3 video inputs (VGA, DVI & HDMI) work on my card.