I have a problem with display. My laptop display dont have brightness at all. After installing i was able to see very very littlebit but basicly black screen. I use now old monitor connected to laptop and with it everything works ok. My laptop is Acer Aspire 5736Z. So if someone knows a solution to my problem please help me.

edit: my first installation so im lost

I've split this out into a seperate topic.

Screen brightness is usually set by the BIOS, and on both systems I've had the BIOS has also managed the setting of the screen brightness.
Have you tried using the hardware keys (usually accessed through the Fn key) to change the screen brightness?
Also, have you ensured that KDE Power Management is enabled?