Brightness I have Compaq v90 monitor its brightness gets on and of, when i decreases it then it becomes little OK.

To help you change the brightness and contrast settings from the LCD monitor, please follow the instructions mentioned below,
The control buttons are located at front panel of the monitor. The Brightness Button is used to select the Brightness/Contrast adjust functions. Press to switch functions or adjust settings.
To decrease the brightness or contrast press (-) button & to increase (+) as per your adjustment.

GuruAid.com

Press the menu button and select the brightness,try decreasing the brightness.Also try lowering the constrast and other color.Hope it works.

Decreasing Screen Brightness (FN+F9)
Press and hold the FN key, then hit the F9 key to decrease screen brightness.

Increasing Screen Brightness (FN+F10)
Press and hold the FN key, then hit the F10 key to increase screen brightness.

Push the 'OSD' ("On Screen Display") button on the bottom-edge of the monitor.
Use the LEFT/RIGHT buttons to select BRIGHTNESS or CONTRAST.
Use the OK button to choose that selection.
Use the LEFT/RIGHT buttons to decrease/increase the BRIGHTNESS.
Use the OK button to confirm the setting.
Use the LEFT/RIGHT buttons to select CONTRAST.
Use the OK button to choose that selection.
Use the LEFT/RIGHT buttons to decrease/increase the CONTRAST.
Use the OK button to confirm the setting.
Push the 'OSD' button to exit from the OSD.

You need to decrease the brightness of your screen by using the buttons on you LG monitor. Push the menu button and then navigate to and select brightness. Now use the left or right arrows to either increase or decrease the brightness.

All the best!
damnor01

Here is a manual for a Daewoo Monitor. On page 3 it indicates that there are buttons that show a right and left arrow above it. When you have the brightness menu highlighted press the left arrow button to decrease the brightness.

Decrease Brightness (fn+f7) The fn+f7 hotkey decreases the brightness of the notebook screen. The longer you hold down the fn+f7 hotkey, the more the screen dims. Decreasing screen brightness conserves power. » To increase screen brightness, press the fn+f8 hotkey.

Increase Brightness (fn+f8) The fn+f8 hotkey increases the brightness of the notebook screen. The longer you hold down the fn+f8 hotkey, the more the screen brightens. » To decrease screen brightness, press the fn+f7 hotkey.

Press the menu button on monitor select the brightness press the menuside button increases or decreases.after select exit oress the exit button on monitor.

There are a couple of possibilities and none of them lend themselves to DIY repair. It can come from arcing in a component trying to fail; you may be able to hear this (if present) by listening closely near the rear of the housing, preferably in a quiet room and near the cooling slits.
Another potential source is what is called a 'cold solder joint' that may look and even measure OK until a little more current is flowing through it.
Neither one is something most users should try to deal with unless you have some technical background since having a powered, open, circuit board can be very dangerous; there are voltages greater than 20,000 volts and several other innocent looking places with many hundreds of volts with sufficient current available to kill.
The only thing you should try on your own is cleaning the guts free of built-up dust that naturally accrues in any high voltage device. Pull the AC cord, ignore overnight, then remove the few screws you will find, often behind the bezel and perhaps a couple in the rear near power cord and video connections/cable.
I like to do this with the monitor laying face down on a soft surface so with most housing you can simply lift the housing free of the bezel and put it aside. With a vacuum cleaner and a clean paintbrush, clean all the areas you see that have obvious build-up of 'fur.'  Try not to disturb any parts in the process though, some are fragile. If the bottom of the circuit board is visible, clean that too and look for any dark brown areas caused by heat. These can become conductive if approaching black in color.
You will see a fairly fat cable leading from a black lump on the circuit board; this is a transformer responsible for producing the 20-25,000 volts. If the unit has been off overnight, you can clean enthusiastically around the rubber cap you see on the side or top of the picture tube; this is a good leakage point for high voltage.   
If you do this and it didn't help, you will have to find a surviving CRT monitor tech to take it from there.   

on the front of the monitor there are key buttons naming menu, ok button and left & right arrow marks buttons first press menu button then go to brightness then by using arrow keys you can increase & decrease the brightness once you are finished decreasing r increasing press ok button.& there are many other settings you can change like contrast etc....