Why is my screen turing off and on every second?

[Melody]

As soon as I was done upgrading to windows 10, I logged in to my pc. It brought me to my home screen but for some reason my screen keeps turning (black) off and then back on again. I've tried to wait it out thinking that maybe the upgrade wasn't finished. I've waited for an hour and a half watching the screen turn off and on. Finally i pressed the shut down button and waited for a while before turning it back on and logging in. To my horror my screen is still doing the same thing, blinking off and on again. I'm really upset and worried. Anyone help, please!