The monitor cable should be connected to the GTX 660 Ti, not the motherboard.
Do you have the PCI-E power connected to the graphics card?
If this is not your issue, you can get back to where you started by reverting your BIOS to default settings.
Search your motherboard manual for "CMOS".
There should be a jumper that will clear the cmos.
The computer must be off when you do this.
Short the jumper and then open it again before starting the computer.