ViewSonic VA912 half screen dead after 30 minutes

well if you don't see a lot , your backlight is dead:), easy to repair since you propably get 3 screens which fit when you search for it and every screen is just an oem.... :). except the special expensive once. Take notice if your screen connection is left or right sided and besides get it removed and placed is by unscrew some screw and then comes the uncliccing parts; Use some a sharp screwdriving(with some tape on it to avoid get ugly points).
It's just clickwork, don't be afraid to ruse some strength.
good luck

that will lcd screen problem

You have set too high resolution for your monitor. Follow these steps to correct the problem.

1. Switch on the computer.

2. Before you see the Windows logo, press F8 button several times. You will get the boot menu.

3. Select the option 'Enable VGA mode' with arrow keys. Press enter.

4. Computer will boot normally, but with larger icons.

5. Open Control Panel --> Appearance and Themes --> Change the screen resolution.

6. Set the screen resolution to 1024 x 768 (or something close to it).

7. Apply the settings and restart the computer.

This will solve your problem. Wish you Good luck!

VA912 does not have built-in speakers, are you sure you have the correct model number, here is the spec for VA912: http://www.superwarehouse.com/ViewSonic_VA912B_Black_19_LCD_Monitor/VA912B/ps/623497

It probably isn't worth repairing as the cost will exceed what you would spend on replacing it.

Look for bad caps, see example here: http://s807.photobucket.com/albums/yy352/budm/Viewsonic%20VX2235W/

It is probably the power supply, or the inverters.

Similar problem with solution, though it requires you to know something about electronics.
http://www.badcaps.net/forum/showthread.php?t=6876&highlight=*va912*

This is usually a bad capacitor problem. They would need to be replaced, or get a new monitor. Some shops will work on them, but you have to weigh the cost vs buying a new monitor for almost the same price.

There are some websites on repairing your own, but you need to know a bit about soldering and such.

i turn on after 30 sec turn off that happen all the time

It is due to logic board , component defect.