Why dont you try removing all non-essentials, like hard disks, dvd-rw, pci(e) cards including the graphics card, and see if your PC turns on that way. Make sure the 24-pin and 8-pin power connectors are seated properly.
Of course, with no graphics card installed, used the on-board one, so your monitor will be connected to the motherboard's vga/hdmi.
Does it work that way? If so, try reinstalling the 960 again.
If it doesnt work with the 960 installed, then you have a possible suspect.
You'd need to test the card after that.