"i have a 50 inch lg model 50pc3d-ue it started flickering a little then the picture would come back on. Now the tv only flickers and sometime you can see the outline of the picture, it is mainly dark"

Sounds like the backlight has failed.

How easy is that to fix?

Due to the high number of Flatscreen problem related to Bad caps, usually bulging in Power supplies, I would say to try first, It is Quick, Free(if mechanically/electrically inclined), Search on Youtube type sites and search Flat screen cap replacement, may even have your model, Radio Shack Makes a Desoldering Iron with the Vacuum Bulb, Personally, this type works better than solderwick or soldepult types, they all work, you don't want to damage a circuit trace/board. Practice on any old circuit board and remove and resolder a capacitor sucessufully, then do it to your Tv, don't add problems. Good Luck.