Generally speaking, there are three possible source of faults
- lcd panel itself: in that case, forget it. The only practical option is to change the panel itself.
- power supply: if the monitor doesn't turn on at all, or suddenly shuts down after a few seconds/minutes of use. This is often caused by blown/leaky electrolytic capacitors. Usually can be fixed by "recapping" the power supply board. Warning: working with power supplies, especially on the "hot" side requires some precautions. In most cases, the damage to the capacitor is visible: bulging or open top. After a few years of use, leaky capacitors are the most frequent cause of problem.
- control board: if the mointor displays garbage, flashes, shifts in color, the control board is likely the cause of the problem. Same issue with electrolytic capacitors + issues with solder joints on the controller board components. Heat is the culprit here, especially if the monitor is set up to do the scaling internally. Inspect solder joints. If the controller is a BGA, it may need to be "reflowed" (in lay terms, cooked so that the solder melts and reconnects the dots). Manufacturers provide reflow temperature curves for example here
http://www.altera.com/literature/an/an081.pdf but some people have had successes with lighters or candles (not that I recommend that - a controlled hot air gun is better, then a pre-heating table. then an oven.
Any semi competent technician should be able to check those things for you. The problem is whether it is economically viable for them (or you) to do so. I am in the process of fixing one of my 30" monitors and stumbled upon hotglued connectors. They are a pain to remove properly and I'll lose several hours finding a reliable connection replacement. Doesn't matter because it's my monitor, but if I was doing this for a third party, that wouldn't make sense.