How Does It Turn On?

my boyfriend found this tv set out on the curb. he brought it home and the first time we plugged it in to see if it worked, it turned right on. so we set it up on our bedroom entertainment center, thinking it worked just fine and someone was only being wasteful in throwing it out. however, now we can't get it to turn on again. we discovered the main Power button in the back, which turns on a yellow light on the front of the set when it's pushed in. when the Power button on the side (near the Volume and Input, etc buttons) is pushed, this light turns green but the screen does not turn on. the light above the aforementioned light has not turned on at all. when the Main Power button is sticking out (which we have assumed to be the OFF position), there are no lights on and nothing happens when the side Power button is pushed. also, we don't have the remote, of course.  is there a trick to turning this thing on or was the first time a fluke?