If you're referring to the base of a laptop, once the screws are out the bases are secured (usually) by a series of internal plastic clips. I have a very thin, screwdriver shaped hard plastic tool which will unclip them (have to slide the tool into the join then twist). If you're not too worried about the finish, you could try a thin, blunt ended knife. Once the first clip has released, just run the 'tool' along the join until it stops at the next clip. Another twist and away you go! Take the battery out before you start.