After activation, QuarkXPress verifies the validity of the activation key each time it is launched. If QuarkXPress fails to detect a valid activation key, you must reactivate the software by contacting Quark customer service, submitting the online form, or faxing the reactivation form.
You must reactivate QuarkXPress if you make a significant hardware change (such as changing the Ethernet address on a Mac® or changing the computer processor) or if the activation mechanism is damaged in some way.
You can re-activate your license online or through chat by going through the link - Online Reactivation
If you need to reactivate your copy of QuarkXPress, reactivate it within 30 days. After 30 days, it will run only in demonstration mode or reduced functionality mode. For more information on Demostration mode or reduced functionality mode go through the link - Reduced functionality mode