Viewsonic VA912b. Monitor will only turn on for a

you might need a new moniter that 1 that you are using is knackerd

Look for bad caps as shown in my pictures, common problem in all brands of LCD monitors.
http://s807.photobucket.com/albums/yy352/budm/Viewsonic%20VA912B/

Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed monitors to get some ideas what to look for: http://s807.photobucket.com/home/budm/allalbums
Post back what you see inside so we can guide you further and it will help out other people in the future also.
http://www.badcaps.net
http://en.wikipedia.org/wiki/Capacitor_plague

Please see my pictures here if you are going to DIY repair: http://s807.photobucket.com/albums/yy352/budm/Viewsonic%20VA912B/

Common problem in LCD monitors, see other failed Viewsonic and other brands in my albums.
Please post back what you find so we can guide you further.
http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.badcaps.net

I will assume that you already try this monitor with other PC already, if that the case, you will need to open it up and inspect the capacitors in the power supply, look for caps with bulging top, see pictures here: http://s807.photobucket.com/albums/yy352/budm/Viewsonic%20VA912B/
Post back what you see inside so we can guide you further.

Try this first. Unplug the monitor power. Let it set for a few seconds and then plug it back in. This corrects this problem most of the time. If that doesn't work, try doing the same thing with the video cable. Disconnect it from the PC and then reattach it. The connections may have gotten corroded and are not making a good contact.

Hope these help you. because beyond that you are looking at either replacing the monitor or the video card.

Rich

There are two places to look for the problems, the backlight inverter board and the power supply, look for burnt parts, bad capacitors, etc.
http://en.wikipedia.org/wiki/Capacitor_plague
Please post back what you find.

it seems that there is a problem in the lcd back light or may be in power supply section

Could be a few things.

It could be the resolution settings.
It could be that your monitor isn't connecting to your computer. In this case you would have to get a card for the monitor to plug into.
It also could be that it's not supported by the OS.

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*

the capacitors in the monitor give out have to see a technician