If you're sure you've installed the latest version of Flash, take each of the following steps that you haven't already tried. After each step, relaunch Safari and test. For a "missing plug-in" error, start with Step 4.
1. If you're getting a "blocked plug-in" error, then from the menu bar select
▹ System Preferences… ▹ Flash Player▹ Advanced
and click Check Now. Quit and relaunch your browser.
2. Triple-click the line below to select it:
Right-click or control-click the highlighted text and select
Services ▹ Open
from the contextual menu. A folder should open. If there is more than one item in the folder with the words "Flash Player" (not "flashplayer") in the name, open the respective Info windows, check the version numbers, and delete all except the latest. You may be prompted for your login password.
3. Re-download and reinstall Flash. Download it from this page: