Cleaning oil pickup screen etc. or how do you remove the oil pan?

Because of so much sludge etc. in the oil system, the oil pickup screen gets covered with debris causing the oil light to come on. I have jacked up the car, removed all the visible bolts from the oil pan as well as the three attached to the bell housing, but the pan will not drop. Also I jacked up the engine to get above the stearing rack / cross bracing. What could I be missing?