You didn't list the motherboard.
I guess the main question I have is if everything was running stable and you were getting great fps why on earth would you change the NB settings and the cpu voltage??? Do you have a clear Cmos option with your MB? I would shut down unplug the power supply and remove the battery from the MB , that should rest everything. I think that changing the northbridge settings affected the pci-e slots and therefore the video card since the northbridge controlls the pci-e slots and the video card is plugged into the pci-e slot.