I wasn't able to start my PC for a whole day.
The motherboard made weird beeping noises when I tried to.
Today I got the tip to look up the motherboard and what the noises mean. My brother did that for me.
What fixed my problem was...... unplugging my keyboard.
Apparently it was blocking the motherboard from working. So now I'm using a USB keyboard that I had lying around.
I hope that was the root of the problem, but I fear I'm not done with this yet...