A pending contest will be locked if you do not select a winner 14 days after the contest ends. To select a winner, the contest has to be unlocked, which will open it for another 14 days before it is locked again:
1. Go to your contest's page.
2. Click Unlock my contest on the top part of the page.
3. Click Confirm Payment on the pop-up that will appear to proceed to pay for the $5 unlock fee (varies across currencies).
The prize for locked Guaranteed contests will be distributed among the qualified entries if a winner is not selected.