It seems you have tried both HDMI and DVI cables so chances of there being a fault in both cables is slim but have you made sure the HDMI/DVI cables are seated into the monitor properly? Also could it be a faulty monitor affecting both HDMI and DVI inputs? I don't understand your "cpu power cable" comment because CPUs do not have power cables, they fit directly into the motherboard CPU socket and get their power from there. Did you mean "GPU power cable"? If so then can you see if there is a fan on the GPU and, if so, is it spinning around?
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