Some systems use to have plastic faces that snapped off and then screws behind that to slide the case open. Most common was 3 screws for the 286 one in center and one at either corner of metal desktop case. Look at the face of this unit and look for plastic latches that hold it on. Should be able to pop the face off with flat headed screw driver... ( Only do this if you see an entry point for a screw driver and the plastic locking latches. I wouldnt start prying on any gap you find unless you dont mind breaking the face off.)
Also some generic boxes I came across had 4 screws under the unit, one at each corner, that had to be removed and then the metal lid would slide back.
HP and Packard Bell also had some with levers, but yours is not that make.
