Dell inspiron 1420 Black screen

About 3 months ago my laptop screen light started going out and i would restart the laptop and it would work fine 

I could shine a light on it and see that everything was still working the way it was supposed to 

now when i turn on the laptop the screen lights up the way its supposed to for about a second then gos black i can still see it working if i shine a light on it 

I did the LCD BIST and all the colors were showing up but there was no light 

so im just wondering what i need to do to fix this 

any help with this will be greatly appreciated