Want to hang LCD TV on wall...?

above a fireplace, the only problem is and its a major problem is that their are no support beams behind the wall, i have no idea why, the wall is about 4 and a half feet wide and about 5 and a half feet high from the mantle to the ceiling, all that is their is the drywall, its the only place i can put the tv because of the room setup, i know at the corners or the wall their are some type of studs wether they are wood studs or the metal framing, i know its possible to get this done but want to know the most effective and safest way to mount this tv on the wall without having to worry about it coming down, i could post some kind of picture so you know what the wall looks like if need be but hopefully i explained good enough, any and all information will be greatly appreciated!!! Thanks in advance!