dim screen cant brighten

Alright guys I always replace my own screens but this time I replaced it when I turned it on it was fine but I was having trouble getting back on so I took it off and put it back on and it became very dim I tried going in the settings and changing things but that didn't work so I finally just decided to put my old screen back own and that screen started doing the same thing so now I dont know what to do because im sure its not the screen at this point. Any help?????