The screen goes very dark within a minute after booting up = I can just barely see the menu page

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.