I recently moved parts from a retired PC into a new case hoping that I could repurpose them. When I press the power button, the problem mentioned in the title occurs. The motherboard's RGB led is still glowing when the case has power supplied, so I don't think the motherboard is the problem. I tried reseating the RAM and unplugging the GPU, but I got the same result. A light on my motherboard flashes yellow for a second alongside the CPU fan spinning.
https://pcpartpicker.com/list/4NQhgt
This is a list of everything in the case at the moment.
https://pcpartpicker.com/list/4NQhgt
This is a list of everything in the case at the moment.