Download the offline installer here: http://fpdownload.macromedia.com/get/flashplayer/current/licensing/mac/install_flash_playe r_11_osx.dmg
If it won't download directly, right click and "Save as". DO NOT mount the DMG or run the installer yet!
Go to: Mac HD/Library/Internet Plugins
Trash the Flash Player.plugin file from there
Go to: Mac HD/Library/Application Support/Adobe
Trash the Flash Player folder (the whole folder)
Empty the trash
Mount the DMG and run the installer.
BEFORE opening any Flash content in Safari, open Safari>Preferences, and check the Security tab to make sure "Allow all other plugins" is checked.