Laptop Problems

Hi,can anyone advise and help me with my laptop which is about a year and half old.
I went to use it and if I am running on batteries then the screen is not as bright as if I am charging and plugged in. I guess its a power saving thing. I went to use the laptop today and the screen brightness wont increase when I put the charger in so its not as bright. It use to and it is charging. How do I fix this as I think I have tried every button, however, the f7 and f8 button which show the brightness icon up or down I cant seem to work. Im not a computer wizzard. Wondering what Im doing wrong.
Any help appreiciated as my eyes are straining.
Thankyou for your answers.