My computer powers on with RGB lighting and fans running, but there is no HDMI signal and neither the keyboard nor mouse receives power. I've checked the cables, storage drive, BIOS, graphics card, and power supply, and I've also tried reseating components. On a few occasions, moving or reseating something inside the case made the computer work briefly, but it eventually shut down again. Reseating the GPU helped most recently, though only for a few minutes. There is some GPU sag, but the case is on its side whenever I work on it. I'm not very experienced with PC troubleshooting, so I'd appreciate a clear process for figuring out which component is causing the problem.
3 Answers
Start by reducing the system to its minimum components: motherboard, CPU, cooler, power supply, and a single RAM stick. Disconnect the storage drives, graphics card, front-panel accessories, and other peripherals. If the processor has integrated graphics, connect the monitor to the motherboard video output. A working board should usually indicate missing RAM with a diagnostic LED or beep code. Then power off and add one component at a time, testing after each addition. That can identify which part or connection makes the system fail.
Disconnect the case’s front-panel USB connectors and other unnecessary front-panel leads from the motherboard, leaving only the power-switch connection if needed. A damaged USB port, cable, or switch can short the board and prevent startup. Make sure the motherboard is mounted only on the correct standoffs and that no loose screw is underneath it. If the computer works outside the case with the minimum hardware installed, the case or one of its connections may be causing the problem.
Because the fans and lights turn on but USB devices and video do nothing, the system may not be completing its POST hardware check. Reseat the RAM and the main motherboard and CPU power connectors, and inspect the slots and connectors for damage. If your processor does not have integrated graphics, the monitor must remain connected to the graphics card. Also check the motherboard’s diagnostic LEDs or listen for beep codes if a case speaker is installed.
I’ve tried testing the RAM one stick at a time, along with checking the power connections and drive, but I’m not very familiar with the rest of the minimum-component process.