Dark sreen I replace the screen but when I put on the screen is dark I see in the background the logo

If half screen is affected it will be either a board (LCD and Plasma have different names) but in those one board drives each side of the screen unit--worst case is the display panel itself which is fatal from a cost point of view.

you need to press either the #5 or #6 preset button while the deck is in standby mode. putting the deck in standby mode should tell you which button to press.

sounds like you are in night mode.
tools>settings>display>colour mode

When you say screen goes very dark when it booted to windows so it means that when you turned on the laptop when the dell logo flashes the screen was fine? if thats the case could you please try this. after turning on the laptop you will see the dell logo flashes immediately keep tapping on F2 and then it will show you the BIOS setup utility, please check if in BIOS setup display goes dark as well. If yes then try this, after turning on the computer when dell logo flashes keep tapping on F12 to boot menu then select utility partition to run the diagnostics. Please run test on the LCD check if display goes black when running the LCD test. Then try this when you sees the dell logo keep tapping on F8 to boot in safe mode check if in safe mode display goes very dark. Try this too, boot in F8 then select last known good configuration check if the settings on your display will be fix. If you can boot to safe mode no problem then uninstall the display or video driver. then restart computer.
You can also try to connect an external monitor if you have one just try to isolate if issue is on the LCD or the video card. If the display is dark as well in external monitor then video card needs to be reseated if fails then replaced. In situation like this most video cards is integrated to the motherboards. So replace motherboard.

replace the drum unit (toner) your drum is weak causing dark background

press F5 in the keyboard the light should be back or check the keyboard in the computer in the top botton where you see a sun design press that one you shoul have two of those 1 for put the light dark and the other one for put the light back good luck

If it got wet, you can bring it to any Apple Store. Nine times out of ten they will replace it for $150 to $200 dollars. Unless they determine it is a manufacturers defect and you are still under warranty, then you want have to pay anything. they will usually just replace it for you.
Otherwise, you may have to pay up to $200 for a replacement.
Hope this helps...Let me know...
enov8

Try the Magic Focus option on the menu screen found under "Picture". Make sure the TV is on for 20 minutes before activating this option. It is also best to run this when the room is dark.

Have you adjusted the brightness? Amend where necessary
Does it happen even on startup? Yes = Monitor Failure repair/replace. No=Graphic settings

Problem is with Invertor Board maybe defective 2SC5707 transistors.
Samir