Quark won't open. I have shut down, completed

This is for Quark on a Mac. What you could do is go to users then which ever user is the active one then library then preferences then quark then QuarkXPress 6.0 (or may say 6.5) in this folder is a file called "XPress Preferences.prf" move it to the trash (Do not empty the trash if it does not work you can replace the file back into the preference folder) and then start up Quark, it should rebuild the file.

Please note your preferences will be back to default and you will need to reset them.

Hope this helps.