Laptop Monitor Failure

[Blookah]

I have an Hitachi laptop thats about 8 years old. The monitor will not come on but when I plug into an external monitor I can view the screen. What might cause this and how do I get the actual laptop screen back up?
Thanks,
Blookah

[merlin_2]

has the slider/ screw knob  on the side of the case been turned down?

[jonah]

Another possibility could be with 8 yrs of opening and closing the laptop, the ribbon/flat cable from th MB to the screen has finally given up the ghost. All it takes is one control "wire" to open up.  

[2k dummy]

Look at the "F" keys across the top. One, possibly two, will a symbol representing a monitor. If there are two, one will be for the backlight and other will be for monitor select. Hold down the Fn key and press the monitor select key. You might have to press it more than once. You can select laptop monitor, external monitor, or both. You probably have external monitor selected.