Maybe there are no screws on the other side, if there are you may have to remove as many panels from the case as you can and hope you can then reach those screws. Do keep in mind that Compaq probably doesn't want you doing this and may have designed the system in such a way that it's impossible to remove the hard drive with just a screwdriver (of course they'll have some kind of superstrong bolting robot that can open the case in case of RMA).