Update on Computer Troubles
The problems were caused by the mysterious deletion of /usr/bin/X11 from the PATH. I added the necessary directory to .bashrc, but I'm not sure how to add it on startup.
I'm using a two-year-old Lindows—now it's Linspire—system. It used to start up and load KDE by itself but now I have to start it in text mode and then type startx.