No desktop on startup just green pixels.

This is a 2010 IMac 3.06 Running IOS 10.8

I Can't upload pic because I am typing this from my phone and apparently the pic is not compatible. So I cant take a screen shot. But I have white screen with Apple icon in center as if the computer is in startup mode. but there are 15 lines of green pixels in a plaid pattern going vertically down the screen. Have tried unplugging and restarting with same result.

Help.