What are the symptoms of a failed power source on a LCD monitor?

I have an LCD 20" Samsung monitor and suddenly the screen stopped working... my laptop recognized it as an extended monitor and there was power going through it because the blue light on the monitor was blinking, its just that the image wasn't showing... so I took it in to get it repaired and they said it was the power source that was damaged and they did regular "service" and they're charging me a lot in Venezuelan currency and I don't really trust their diagnosis, I mean if the power source was damaged, the monitor wouldn't even have turned on in the first place... I don't know, I'm no expert but I don't wanna be ripped off because of my ignorance on the subject, tomorrow I have to pick it up and pay so I wanna be sure that I'm paying the right value, if not I want to complain or something... by the way this is a Samsung authorized service center in Venezuela