My iMac screen went pixilated then went black

Hey!

So earlier tonight my 27" iMac (2009) went pixilated (green, yellow, blue, white small pixels) then the screen went black, but the computer was still running. I shut it down and turned it back on and I didn't have a problem until recently. After clicking play on a video on Facebook, the pixels returned and the screen went black again. I then proceeded to shut the computer down, but when I turned it back on, this is what I saw (refer to picture, sorry it's upsidedown)

The lines eventually disappeared along with the Apple logo, but the screen remained white for at least five minutes. I restarted my mac again, but the lines returned and the screen stayed white. That was around ten minutes ago and the screen is still white. What's wrong here?

Also, I recently upgraded to Mountain Lion about two months or so ago from Snow Leopard (either 10.8 or 10.8.1) if that's important at all.