I have a Flat screen PL913s monitor. I just replaces the 6 electrolytic caps on the power supply board and now the monitor that was totally blank before works, but only for about two minutes and then I hear a high frequency buzzing sound and the monitor goes blank. If I turn it off and on again, it does the same thing, works for about two minutes, then the sound and goes off. Any clue ? Please help

Check the power supply for bad or bulged electrolytic caps , or replace power supply board.

If you take the back off you might see a couple of electrolytic caps that might be bulged on the power supply board. The power supply board is getting weak, and if you replace the electrolytic caps that will fix the problem. You can also replace the power supply, and you can check at www.partstore.com for a power supply.

Did you inspect the caps for domed tops in the power supply/inverter board yet? Worst case will be the lamps assembly.
If you are going to DIY and already try the monitor with another PC, and have proper tools and know safety precaution then please read on:
Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply (they should be replaced in a set), blown fuses; poor solder joints, 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/albums/yy352/budm/
Post back what you see inside so we can guide you further and it will help out other people in the future also.

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r7406380-tv_training_manuals
Failed TV and Monitors: http://s807.photobucket.com/albums/yy352/budm/

Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague

Capacitors kit: http://lcdalternatives.auctivacommerce.com/ he can make you a set of caps for you.

Or www.digikey.com just make sure to use caps with low ESR, 105c, high ripple current, long life rating such as PANASONIC FM or FC series.
Please leave rating if it helps.

Change the electrolytic caps on power supply, or replace power supply and it will work fine.

You probably have a blown power supply.

The caps on lcd flat screens can go bad and leave you with this condition.

The fix involves removing the power supply board from the inside of the monitor and replacing the damaged cap. I would recommend replacing ALL the electrolytic caps once you have the board out. The caps are inexpensive and someone with soldering skills shouldnt be too hard to find right?

Good luck and be careful!

The problem can be bad caps (bulging top) which is more likely, or bad backlight inverter circuits. Check to see if you do have 12vdc or no bad caps, see example of failed monitors due to bad caps: http://s807.photobucket.com/home/budm/allalbums

The power supply-inverter board is probably at fault. Remove the back cover and locate the standard ac power cord connector. The board that the power input connector is soldered to is your power supply - inverter board. Check the electrolytic capacitors on the board. They probably went bad. A visual inspection is usually enough to find out which ones are bad. They will be either bulging or cracked at the top and leaking fluid. I usually replace all of the capacitors that have the same rating whether they look bad or not. Will save you another repair later. If the caps don't look bad, you can take the board to your local tv repair shop and have the caps checked with a esr tester. It's more accurate and they can be tested with the caps in place. Hope this helps.

I had the exact same problem. The screen went black and the green light flashed. I went ahead and took the monitor apart (scary) and took a look at the power supply circuitry. I saw 6 suspicious electrolytic caps on the board. Three 470uF 25V 105 degree C caps, two 1000uF 10V 105 degree C caps, and one 470uF 10V 105 degree cap. They all appeared to be slightly bulging and one even had a small hole in the top. I decided to replace all of them. The parts cost a little more than 5 bucks. I couldn't find a 470uF 10V cap at my local store so I bought a 16 V version instead, which is fine. Anyway, after replacing all 6 caps, the monitor works as good as new.

If you haven't figured it out yet through a web search, Westinghouse monitoris have problems with blown caps on the power supply board. If you are lucky the problem is minimal and won't require more than replacement of the caps. You won't know until/unless you open the case and inspect the power supply board.

you ave some blown caps on the vga board replace them and all will be well