Monitor Shows pixelated colors then flashes no input and turnsoff

Ok So I'm playin a game online, first my computer beeps once, then the screen looks like it has colors kind of melting into in until it all turns into big pixelled squares. I had sound and dont believe it locked up but I cant really tell to be honest. I powered down the computer and now everytime I start it my monitor gives me a crazy color show then my monitor flashes no input and turns off, after 10 seconds I get the crazy colors again then off again, this repeats over and over again until I turn off the computer. Im hoping its a monitor or Video Card thing I just have if theres a way I could get a definite answer as to which one.