So I was changing the case fans, after I put everything back together, I forgot to plug in the power for the GPU. I turned the pc on and I saw the white LED on GPU power port lid up and heard the fan spins like crazy (I don’t know if it was the CPU fan or the GPU fans), I panicked and immediately turned off the power supply.

Everything happened in less than 2 seconds, I’ve run some stress tests and gamed for a few hours and nothing bad happened (yet?) so I assumed everything is still fine (for now?).

What happens if I had left it on like that for longer? And why did the fan ram up like that?