Okay, I've got my desktop back!
I just used xfs & (entered, about a line and a half of text appeared) and then startx.
Before this, when I checked the status of xfs (using service xfs status) it said it was dead even when I had just started it (service xfs start). Now I got an xfs running message and I could access GNOME. I halted the system, booted it up again and everything was back to normal - I got a graphical login and could access KDE.
I think my problems were caused by running a program in /root without enough memory - not really font-related at all ...