Trouble shooting steps :
1) disable secure browsing in facebook settings if it is enabled (account settings > security > secure browsing)
2) switch browsers (try google chrome, firefox, safari -and any other browser you may have), also make sure the browser is upgraded to the latest version
3) update flash player
4) delete all browser cache and cookies
5) delete flash cache ( done HERE ) click the "delete all sites" button.
6) restart computer
You might also want to check out the Recommended System Requirements