Sorry this does not answer your question, but the 'xorg.conf.back' file most likely has nothing to do with your wireless configuration. The 'xorg.conf' file control settings and configuration information for your X-server (graphics, monitor display, resolution, refresh rate, mouse input, etc.).
This is only an idea:
If you updated your Fedora Core, chances are you may have updated your kernel also. If you update your kernel then EVERY ADDITIONAL driver must be updated with it. These are the drivers you may had to install seperately (maybe video card, wireless, etc.). ... Either undo your update or just redo your wireless setup.