Apparently it's all due to BIOS settings.. you probably have the 750 ti connected to DVI and as far as I know, by default all BIOS chips come in VGA, so when you reset it, the BIOS reverted to VGA, therefore the blank screen. It should have automatically changed the setting to DVI but for some reason did not.
The z77-d3h motherboard has two PCIe slots so you must have both GPUs installed... switch the video cable to the 550ti to access the BIOS and check the BIOS video settings, and compare how it reads both GPUs, and configure the settings exactly the same for both cards, and also check/change the Windows video settings, and set the 750ti as default. If nothing chages after restarting the computer, switch GPUs on the PCIe slots or remove the 550ti.