A severe thunderstorm caused the power to flicker after lightning struck nearby. Since then, the PC powers on and its fans and component lights work, but neither monitor receives a signal. The monitors work normally with a Nintendo Switch. The graphics card was removed and reseated, the RAM was reseated, and the motherboard battery was removed for about ten minutes. Displaying from both the graphics card and the i5-13600K's integrated graphics produces the same result. The system uses an MSI MAG Z790 Tomahawk, and its debug lights cycle through red, yellow, and white before turning off as usual. The PC was connected to a surge-protector power strip. What else can be tested before replacing the motherboard, graphics card, or another component?
2 Answers
A surge strip is not always enough protection against a nearby lightning strike, and a damaged power supply can still spin fans and light LEDs while failing to provide stable power for video initialization. Disconnect unnecessary drives and USB devices, then test with one RAM stick, the CPU, cooler, motherboard, and GPU. If possible, try a known-good PSU with the correct modular cables. Avoid repeatedly swapping parts while power is connected, and inspect the board, GPU, and PSU for scorching or a burnt smell.
Since the debug LEDs complete their normal cycle and turn off, the board may be getting through POST, so try the basic display checks again with only one monitor connected. Test a different known-good HDMI or DisplayPort cable, manually select the correct input on the monitor, and try every output on the graphics card. Also make sure the cable is connected to the GPU when the GPU is installed, not the motherboard video output.
The motherboard’s lights cycling normally is reassuring, but it does not completely rule out a damaged GPU, PSU, or video path. If a different PSU and cable do not help, the most useful next step would be testing the GPU in another system or trying a known-good GPU in this one.