Without knowing why the screen is blank it's hard to guess at the corrective action needed.
But some common problems and possible solutions:
Replace a malfunctioning FL inverter which powers the CCFL backlight in the LCD screen.
Replace a malfunctioning CCFL backlight in the LCD screen.
Replace a damaged or non-working LCD screen.
If the reason the screen is blank is due to a bad video chip on the motherboard - you'll need a motherboard replacement.