Hi everyone i hope you can help me

I switched on my white imac today and the screen had spilt in two one side had my desktop and the other had 2 black and one white vertical stripe,i have also done a screen shot and there is no stripes on that,i would also like to add another monitor (laptop windows 7) so i can see the dock,what has gone wrong and is it expensive repair,i think i have loaded a photo

I have done some research and could it be the inverter,i know it's an old mac but i'm attached to it now

Could the inverter, but if that fails - you don't usually lose just part of the screen.

I've seen this fairly often, and usually means replacing the LCD panel.

And, if you haven't done anything else yet, you could try a PRAM reset.

Try connecting an external monitor - this will tell you if the problem is related to the graphics chip or the LCD. You will need the dongle, if you go to an Apple Store they might let you borrow one to test on a monitor there(?).