Check if your license expired. Just open the license in your favorite text editor and see the issue_date. From this time, the license is valid for version which are released from issue_date to issue_date +360 days. If so, then your license is still valid, but not for that version.
When you have replaced hardware components your license might also become invalid. See How do I get a new license if my computer breaks? for details.
Posted in: Licensing