27" Imac Sudden Black Screen, System Still Running


Hi there, I am NOT a tech savvy person at all! but have a 27" imac, 3 years old. Suddenly yesterday, the screen went black. System still running in background, no cursor in corner. I have read this thread, tried the SMC and PRAM resets, no joy, just makes a noise on resetting PRAM. It has a wireless keyboard and mouse. As always, terrified of the cost of a visit to the store!! Any help would be welcome :)


Do you see any video on the screen? Shine a bright light into the screen. Look at the top for menus, and you dock, or windows/icons on the desktop. You may need to look carefully, or make the room as dark as possible. The video on the screen could be very dim.
Because you can't really see anything much, make sure that you have shut off the iMac completely (disconnect the power cord to make sure), then start up. Wait at least a minute before checking for video. Again, shine a bright light into the screen, moving the light around at different angles and positions, just to try to see any icons or menus.
Do you see ANY images on the screen?
That would mean that you have video, but the backlight, which gives you the brightness on the screen, may have failed.
If you don't see ANY kind of images, even very dim on the screen, then you should try an external display, connected through the Mini Displayport. If you get video on an external display, and still nothing on the built-in display, then the LCD panel may have failed, or maybe the inverter board.
Either way - if some part has failed, and you want it to work again, then it will be time to spend some money. You can always get a quote on replacing the display, or the graphics card. Then, decide if that will be worth fixing. The repair shop MIGHT have some suggestions for that.
You will be able to take it in, and tell them that you have video, but the backlight is not working (that's the dark screen, but you can see images and menus in the screen when you shine a bright light into the screen). You can show off at least a little tech knowledge, and ask the good questions, such as "How can I get the screen backlight to come back on?"
Come back with what you find out :D