I took it apart (it looks rather Frankenstein with the bezel off but all the other parts in place) and reseated the screen cable and now it mostly works. The digitizer is rather nonlinear in the virtual graffiti area with the result that you can only tap on the bottom icon bar when the slider is closed; this may be to do with the fact that all four side screws are missing, or it may be that the digitizer cable also needs to be reseated. Was this a problem before?