Try making sure that the PCI-E freq is set to 100. Make sure that all voltages and freq are set by you and not on auto. With the OC cpu, your board might be clocking up something that the card can't handle and thats why PCI-E freq seems like the most likely cause. You could try base clocks and try OC the cpu slowly and see at which point the card stops responding. Write down the clocks to refer to when this happens.