Unplug everything including any front panel usb plugs etc except for the front panel power switch and the motherboard/psu/fan power, and the GPU if your motherboard/cpu does not have an iGPU. Use the motherboard display output if so.
If it boots. Add devices one at a time.
If it does not boot … it’s a bad PSU.
Make sure you’re using the correct outputs on the PSU if it’s modular.
Unplug everything including any front panel usb plugs etc except for the front panel power switch and the motherboard/psu/fan power, and the GPU if your motherboard/cpu does not have an iGPU. Use the motherboard display output if so.
If it boots. Add devices one at a time.
If it does not boot … it’s a bad PSU.
Make sure you’re using the correct outputs on the PSU if it’s modular.