...you mention that it will not open any files, this indicates that quark does in fact launch?
...with this fact can you create new quark documents?
...have you tried booting in safe mode (shift key on startup), then restarting again to clean font caches?
...are your font folders packed with fonts you rarely use? If so, move them out apart from the system critical fonts, the ones installed by the OS...
...have you removed this file from user > library > preferences "com.quark.QuarkXPress.plist"?
...and this entire folder "Quark" from the same location?
...if not try removing those...
...does quark work fine without the suitcase extension loaded in the quark application folder > extensions?
...does quark run fine when in "safe" boot mode, but not in normal boot?
...are you running 10.4 OS, and have you tried creating a virtual printer, then launching quark?
andrew