Adrian, I hope that was the power button … and not the Input Voltage change switch.
Changing the input voltage will make your power supply go boom, and if it’s a cheap power supply, your whole PC will go boom
I’d suggest you get a light behind there and check it out & keep your fingers crossed that it was just the main power switch, and not the input voltage switch.
What country are you in?
USA & Canada is 100-120V input.
Most of the rest of the world is 200-240V input.