Blackout I have an HP L1902 LCD monitor that after a 2 -3 minutes have a blackout.... the green led on the power buton is on but there is no light on lcd.....

have you been check for a bulging capacitors at the power supply board.

after blackout, check the screen as that. look in to the monitor in side angel,
and if you can see darken live image in that and its working. in that condition, your
LCD panel is working and the problem is no light.
in that case you need to repleace or repair the " inverter unit " in that monitor.
that unit makes the high voltage for back light.

after blackout , you cant see any darken image like as that, and or totally power
goes off , that is different problem. for solve that need advance trouble shooting
and can be need advance repair.

More likely to be bad solder joints on the four inductors: http://www.lesliewong.us/blog/2005/05/02/hp-pavilion-f1703-flat-panel-display-blackout-solution/

Common failure in this monitor is the poor soldering works on the doughnut (4) shape inductors in the inverter board, http://www.lesliewong.us/blog/2005/05/02/hp-pavilion-f1703-flat-panel-display-blackout-solution/

Poor soldering works in the inverter board: http://www.lesliewong.us/blog/2005/05/02/hp-pavilion-f1703-flat-panel-display-blackout-solution/

Here is a website that provides instructions to repair the inverter on a similar model:

http://josepino.com/?howto-repair-dell

Possibly either the backlight lamp or its associated power supply has failed. Power buttons (mostly LEDs) have constant availability of low voltage (for some other circuits too) otherwise they wouldn't 'wake up' on command from a computer as some do.
The blackout could also be due to a failed main power supply so the incoming video is no longer being processed. 

no stays completely blank. yes it is my pcs monitor

When your dell e173fp lcd monitor black out, the led power light are still green color. Normally, this will be the inverter board or ccfl lamp problem. May i know, after this monitor black out, do you have try use the torch light to see any display on the screen? (sometime the display are darkness only and not totally no display, you need see it clearly). Any details on repair lcd monitor please goto this website, http://www.fastrepairguide.com

Can you see anything at on but dimly? If so thats is the backlight tube If you cannot see anything then it is a major fault eitherway a repair shop job I should think