Copying info from this doc: http://helpx.adobe.com/x-productkb/global/trial-software-expired-early.html
Adobe trial software is time limited, and otherwise has the same feature set as the licensed version. Some scenarios can cause trial software to expire early:
- Changing the system clock
- Modifying the executable file
- Attaching a debugger
- Automated virus scans
Trial periods can't be extended. After a trial expires, you need a serial number to install the software as a licensed version. Or, you can install trial software on another computer.
It can't be done. Whatever happened has locked the licensing system and as much as this may suck, only inputting a serial number can release it again. We won't speculate as to why it happened, it could after all be a technical glitch, but that's just how it is. If you have a secondfary computer, try it there. Or you could make a leap of faith and just buy it...