My PC suddenly shut down while it was sitting idle, and since then it powers on for about half a second before the PSU clicks and everything turns off. I recently replaced the GPU, CPU, and RAM, and I have now also tried a different motherboard and PSU. The system sometimes repeatedly powers on and off before staying running, but I have never managed to get an image on the monitor.
The original system was built around a Ryzen 7 5700X3D, a Gigabyte Radeon RX 9060 XT 16GB, 32GB of DDR4-3200 memory, an Asus B450-F motherboard, and a Corsair TX650M PSU. I replaced the motherboard with a Gigabyte B550 Gaming X V2 and the PSU with a Gigabyte Aorus Elite PI 850W, but the symptoms remain.
I have tested one RAM stick in different slots, old and new memory, both GPUs, different modular power cables, different wall outlets, BIOS resets, reseating the CPU and checking its pins, and running the system without drives, case connections, USB devices, RAM, or the GPU. The PC would stay powered on when the CPU 8-pin cable was disconnected, although there was still no display. It also briefly worked while partially assembled, then began shutting down again after I moved it and connected the keyboard and mouse.
Could this be a short, a faulty CPU, an issue with the case or USB ports, or an outdated BIOS that does not support the 5700X3D?
2 Answers
The symptoms may be caused by more than one issue. An immediate click and shutdown usually means the PSU is detecting a short or another protection fault. Since disconnecting the CPU power cable changed the behavior, the CPU power circuit, motherboard, or processor could be involved.
The new B550 board may also need a BIOS update before it can initialize the Ryzen 7 5700X3D. Check whether it supports Q-Flash Plus and update it using a USB drive, without needing a working display. Also test the system outside the case on top of the motherboard box with only the motherboard, CPU, cooler, PSU, GPU, and one RAM stick connected. Leave all USB devices, front-panel connectors, drives, and case wiring disconnected, and start it by briefly bridging the power pins with a screwdriver.
If the board has the correct BIOS and still repeatedly cycles or never posts in this barebones setup, the CPU may have been damaged or another core component may be faulty.
The repeated on-off behavior can also indicate that the PSU is not receiving or maintaining a proper Power Good signal. Since the original Corsair PSU and the replacement unit behave similarly, the PSU itself may not be the root cause, but testing with a known-good compatible unit and its matching cables can help rule that out. Avoid mixing modular cables between power supplies, and inspect the motherboard mounting points, CPU power connector, USB ports, and case standoffs for a short.
I suspect there may be multiple problems happening at once. I have not tried updating the BIOS yet, so I will test Q-Flash Plus and run the board outside the case. Is the repeated power cycling normal if the only problem is an incompatible BIOS, or does that point more strongly to a hardware fault?