I am trying to put up pot lightsan I can't seem to get the junction box out of the ceiling, I have taken one screw out from the box but can't still not get it down can anyone help please??

Provide a photo, otherwise we are all guessing.

Yeah... a pic would be nice... but what kind of fixture was there before you removed it.. if it was a ceiling fan, there may be a brace holding it in connected to the 2 opposing joists. You could carefully cut around the box and take a look and see if there is anything else holding the box in the wall... sometimes people painstakingly reinforce ceiling boxes.