My toshiba screen

Try this:
https://forums.lenovo.com/t5/Lenovo-P-Y-and-Z-series/Z400-Adjusting-the-Brightness-in-Windows-8-1/ta-p/1303113

can be the brightness setting of the laptop's screen..have it change to the appropriate brightness setting then you're all set :)

Every laptop that is coming to the market has a button the bottom left just next to the "Crtl" button. This button says "Fn". On the other hand please find the buttons that are marked with dark Sun or a white sun. These buttons are for decreasing or increasing brightness. Just press down the "Fn" key (or button) and then press the key with the white sun on it. The brightness of the laptop screen will increase.
The keys with sun symbol on it are usually the arrow keys.

Good Luck!

If your screen is that dark when it boots up, you may have lost the inverter that supplies the increased voltage to run the screens backlight. The commands for the lightening and darkening the screen are as follows.....

<Fn> and up-arrow key Increases brightness

<Fn> and down-arrow key Decreases brightness

one of two causes : inverter board damage ( Replace it) or backlight lamp damager (also replace it).

Try going into the control panel and select power options see if there is way to adjust the display brightness or try holding down the "Fn" key and use F7 to increase the brightness

Hi,
No the screen is fine the back light is not working you have replace the back light of the screen to resolve the issue.But before that please try the FN+F6 or F7 keys to control the brightness.

Fn+F1 Decreases the display brightness. Fn+F2 Increases the display brightness

Fn+F1 Decreases the display brightness. Fn+F2 Increases the display brightness.

Push and hold the Fn button and for decrease of brightnes push F7 for increase push F6 . So Fn+F7 dark: Fn+F6 bright.

Arsim