I have performed several installations of Fedora 10 and a few upgrades from previous versions of Fedora to Fedora 10. So far I have had very few problems, but one interesting problem occurred when I upgraded one computer from Fedora Core 6 to Fedora 10.
After the upgrade it was possible to login to the KDE GUI but many programs would fail at launch time. A few, such as Konsole worked fine, but Firefox, Thunderbird and other applications such as OpenOffice would fail. I tried launching Firefox from a command line and it failed but it also displayed an error which indicated a problem with the X window system and invalid colors or fonts.
I resolved this problem by changing to runlevel 3 and logging in as root in order to run the command:
This command deletes the existing X11 configuration and completely rebuilt it.
This problem was most likely due to very old configuration entries in the /etc/X11/xorg.conf file which were not recognized or were handled incorrectly by the current version of X11.