The easiest idea is a messy one. 1) Find your joists and mark them. 2) Set your power saw to 1/16" thicker than the thickness of the particle board. 3) Cut any which way you can in a PERPENDICULAR direction to the joist, and make cuts on BOTH sides of your nails/screws/tacks that are holding down the board. 4) Remove the pieces that you cut out and all you should be left with are 'pieces / sections' of particle board that are still nailed/screwed/tacked to the joists. Having just those small pieces left should be EASY to remove.
IF you decide any other approaches that incorporate the use of a power saw, be MINDFUL of electrical wires, piping, or whatever, that might be secured to the UNDERSIDE of the particle board. Also, be careful of kickbacks from the saw!