That is when the cutscene comes up for the end of act 2. I had the same thing happen at the end of act 1. Only the 1.42 patch allowed me to continue with the game. If you have not yet patched to 1.42, you may need to to continue.
One other option is to use the configuration tool to reset the resolution to 640x480 until after the cutscene is over. This is suppose to be a way around resolution reset problems with windows 98. If you don't have windows 98 it should not be a problem. It did not help me when I had the same problem at the end of act I (I have windows xp).
