I replaced my working Radeon 6700 XT with a new 9070 XT, and afterward the PC would power on for only two or three seconds before shutting off. I checked and reconnected the PCIe and CPU power cables. At one point it stayed on long enough for me to install the new graphics drivers, but it shut down again after restarting, and the power button then stopped responding.
I also reinstalled the old GPU and got the same behavior. The PC shuts down even with no GPU installed. The system uses a four-year-old Corsair SF750 Platinum, an Intel i5-12400F, a Biostar B660 GTN motherboard, and 2x8GB Corsair Vengeance LPX DDR4. The PC was unplugged before the GPU replacement.
3 Answers
Also check for a short or a loose connection around the motherboard. Reseat both RAM sticks and test one at a time, inspect the PCIe slot for debris, and verify that the motherboard isn't contacting an extra case standoff. If it still powers off instantly with minimal hardware and a known-good PSU, the motherboard becomes the most likely failed component.
The PSU is worth investigating. A 750W unit should generally be adequate for this build, but a four-year-old supply can still fail or trigger protection when the system starts. If possible, test with a known-good PSU, using only the cables that belong to that PSU. Don't mix modular cables between power supplies.
Since it also shuts down with the old GPU and with no GPU installed, the graphics card and its drivers probably aren't the cause. Start by clearing the CMOS and loading the BIOS defaults. Then test with only the motherboard, CPU, one RAM stick, and the power supply connected. Make sure the 24-pin motherboard and 8-pin CPU power connectors are fully seated.
It was unplugged before I changed the card, and the shutdown still happens with no GPU installed. I'll try clearing CMOS and testing the system with one RAM stick and another PSU.