Computer runs but no boot screen

Hello,
Today my computer was running hotter than usual due to the summer heat so I've decided to shut off the computer to plug in my side panel fan (which is usually unplugged because I hate the LED light).

After simply connecting the fan to the power cable, I turned on the computer and don't see a boot screen. It's as if the monitor is still sleeping but the entire computer is running. I've turned on and off the monitor and it just says "No DVI signal detected". I'm positive its not due to me connecting cables to the wrong spot since I only plugged in 1 cable... the fan cable.