Why do my eyes burn when I'm on the computer?

How to adjust brightness on ASUS computer monitor, brightness is really low, can barely see?

• I have some kind of ASUS computer, and it happened yesterday. My sister and i were watching InuYasha, and my sister is 8 so when she plays the computer, she has to bring the mouse to her size if u know what i mean, and when i play i push the wire that the mouse is attached to, down,and then the computer monitor just went out! like -poof-. but the computer wasnt off,i could still hear the video of the smosh video i was watching o.0 . so yea.. The next day my brother tried to fix it, he wasnt much help, but he thinks that something is wrong with the brightness, when i turn the monitor on , off , and then on again, u can see normally for about 1 sec and then it goes back to dark, BUT for about 5 seconds after it goes black you can sorta see the desktop alittle but it's very had to see, you have to sorta squint your eyes to see it, after that 5 secs is over, it goes black again. PLEASE GUYS, I NEED HELP FAST! and just in case u guys are wondering, im on another computer, btw when i said i was trying to bring the wire thing down, im not sure but i think i pressed something, at the bottom right corner, theres like 5 buttons there, im not certain if i press on of the buttons though, or theres something wrong with the computer, HELP! i've had the computer for about 1 year and a half, and this has never happened before! and im not that of a computer nerd, but when it takes forever to figure out, and cant find out, i get really desperate and search everywhere! HELPELPELPELPEE P-P-PLEASE? T.T

• Answer:

  Press the Fn key and hold it as you press the up button on the arrow keys.