If you downloaded leJOS 1.0.2.RC6 you should download and install 1.0.2.RC8 instead as there is a bug in RC6 that causes the RCX to ignore sensors and buttons for several minutes. Apologies for the inconvenience - Paul Andrews. (23 years ago, 2-Sep-01, to lugnet.robotics.rcx.java)
(...) Ahem. Similar bug in RC8 too. I'm fairly confident that RC9 has fixed them all. Apologies once again :-( Paul (23 years ago, 2-Sep-01, to lugnet.robotics.rcx.java)