Anyone know how to repair LCD TVs?

I hve 2 15" widescreen HD (some I’m told) LCD tv’s neither of them work…

Basically you plug it in, it switches into stanby so you press the on button the light chnges to green you can hear it kind go ping (if you know what I mean) but there is no picture or sound and does not look like the screen is switched on at all…

so any ideas?