The solution I am about to describe refers to a backlight problem, which is most common in Dell 15,17 & 19" monitors. The symptoms are as you describe:
- You power on the monitor, the green on/off switch illuminates and the display works for approx 1-2 seconds and then goes blank.
- The green on/off switch stays illuminated but the screen remains blank
- If you shine a torch into the LCD matrix you can see the display being rendered faintly
- Switching the monitor off and then on again illuminates the display again for 1-2 seconds before going blank again
This is a backlight fault and is most likely to be caused by the failure of two of the four driver transistors used to light the lighting tubes in the LCD Matrix. This fault is easy to repair if you (or a friend) have a soldering iron and a voltmeter.
Inside the monitor there is an inverter board that acts as a power supply for the monitor and the logic necessary to control the backlights (illumination and brightness control). There are four lighting tubes, which are controlled by two lighting circuits (two lighting tubes per circuit). At the heart of the inverter board is a chip that monitors feedback from the two lighting circuits and closes the back-light circuit down if either of the lighting circuits fail, thus any component failure will exhibit the same symptoms.
The transistors which fail most often cost pence to replace (types C5706 or C5707). However, their failure in unlikely to be the cause of the problem. My first crack at fixing this fault, by replacing the transistors, resulted in them failing again within 24/48Hrs. The cause of the problem will be dry solder joints or loose connections on the high-voltage side of the circuit, usually on the backlight transformer in the effected circuit. If you re solder each of the connectors on the transformer you will save the transistors from blowing again - the transformer generates 1,400Volts for the lighting tubes and at this voltage, arcing across the a dry solder joint, will quickly destroy the transistors again.
No soldering iron? - A complete inverter board replacement is also reasonably cheap and easy repair. These are widely available.
Sorry of this is more detail than you expected but it may help others reading this article.