Green colour and horizontal lines

I have a sony trinitron tv and was given it for nothing. It works fine other than there is a green tinge over the whole screen and some very bright horizontal green lines spaced down the full height of the screen. The spacing of the lines varies, getting bigger towards the bottom, I think! I think there must be about 15 of these lines. I should also say, if it is any help, that the green colour comes on when you turn the monitor on, but before the tv signal actually comes through. Does anyone have any thoughts about what is wrong with it?

thanks very much in advance