If you're on Yosemite (OS 10.10.x) and the installer is completing successfully, but Flash Player just isn't working in Safari, you may need to do the following:
Open Safari, and choose Safari > Preferences from the top left corner of the screen.
Check "Allow Plug-Ins" if it's not checked already
Click the Website Settings
Choose Adobe Flash Player, and click Allow
You can log into your computer with administer account.