This is a hardware issue--either the inverter is going or the backlight on the LCD (since it goes in and out, I tend toward the former). Does moving the lcd screen up and down have any effect? If so, it could also be the little flexible cable connection the screen to the motherboard
In a pinch, you can still hook up your laptop to a monitor---the afformentioned issues are not related to your PC or video operation, just the display on the LCD
An inverter is sometimes separate, and can be replaced easily enough (prices range greatly from motherboard to motherboard--$30 to $130). Sometimes they are integrated on the motherboard.
A backlight is pretty cheap, but hard to replace. About $40.
the ribbon cable might be lose or broken--loose easy to fix, broken...doubt you can find a replacement, and would need to buy the LCD , which is very expensive)