Chosen Solution
On my 27" Apple Cinema Display, the screen is blank but if I hold a light up to the screen and I can see the background image. What need to be replaced/fixed? And do you have the part?
armcomdes that means your backlight has failed. You would have to disassemble it and check to see if you have appropriate power on the connector. If yes you know it is the backlight inside the panel that has failed. If not then you will have to check the backlight circuit on your logic board. Let us know what number the LCD display is and post some good pictures of your logicboard so we can see what you see Adding images to an existing question - iFixit Repair Guide. Something like this guide Apple LED Cinema Display 27" LED Panel Replacement - iFixit Repair Guide should get you there.
