How do I fix my TV that will give an image after powering on, and then make it go so dark you can't see it?

If you can see the image as you say its dark that should be backlights are faulty

The LCD and the back light is not working for your TV and there is also a LCD and back lighting issue too..

You need to do some troubleshooting first. Turn the TV on make sure the room is dark take a good flashlight and shine it at the screen and flip through the HDMI inputs. if you don't see an image then it's most likely your main board you can have that fixed or repaired at pts electronics. If you do see an image then the backlights aren't working and you need to check the outputs to the backlights at the main board. The TV is worth fixing

go nto the main setting and clear everything and reset it you will have to start from new but the brightness will improve

When the TV is on, if you look at the screen and can see dark images, then you will need to replace both the inverters. The inverters drive/power the back light inside the LCD to show the images. You may have to try and different channels and or inputs to truly see if you can see dark images while the TV is on. If you are hearing audio from a channel or an input then you should be able to see the dark images if just the inverters are bad.
If the screen is dead black without any dark images, then typically your LCD screen/module is bad.
If the TV powers up (power supply is good), you have audio and the remote will work with the TV (the main board is good), the only parts left is the inverters or the LCD screen/module.
I can get you LG part numbers if you need them.

It may be the closed captioning it happened with mine. I simply turned off the CC on the TV.

Try hooking the TV to a different outlet fed by a different breaker. Does the problem go away? If so, the culprit may be a wiring problem in your house that is causing the TV not to get enough power unless the dining room light is on.If in doubt, consult an electrician to make sure both the dining room light and TV outlet circuits are working properly.

you could be on the right track get some freeze spray and go around all the parts to see if you can make it act up, same with heatgun or hair dryer when first turned on heat one area at a time to narrow your problem down

Is there a simple fix for this, yes The picture is very dark it is mostly due to 1 power supply output is low. 2 voltage on crt g2 pin is low. 3 video output supply is low. 4 some components in luminance section might be defective or loose. 5 finally crt getting weak but as you have bought in 2004 so possibility is rear. good luck

not sure but you could have a bad color wheel i would suggest a service call from your local shop