Flash Player may fail to install due to incorrect permissions in the registry. Before you download the Microsoft tool and follow these instructions, first read this TechNote "Troubleshoot Adobe Flash Player installation for Windows" (TechNote tn_19166).
Additionally, if you don't have administrator access, then you may not be able to install Flash Player successfully. Permissions can be tricky but, in general, you should be able to install and use Adobe Flash Player if your system administrator gives you full access. Windows administrators should be familiar with "Registry permissions required for Flash Player install or update" (TechNote tn_19148).
Using the SubInAcL tool from Microsoft to fix permission issues in the registry has solved installation errors for several products including Flash Player.
Warning! The following solution involves the Windows System Registry. Editing or manipulating the registry incorrectly can result in serious system damage which may require reinstallation of the operating system. If you are not comfortable editing the registry, then take your system to a professional. If you choose to proceed, then it is essential that you create a complete system backup and a Windows System Restore Point before proceeding. Adobe Systems cannot be held responsible for damage resulting from this information.
You must have administrator privileges to successfully complete these instructions.