Issues:
- During Flash Player installation, you see the error message : “Failed to install” or ”Failed to register”
- Your Flash Player installation finishes with no error, but you cannot view Flash content in Internet Explorer.
- Some sites tell you that you do not have the correct version of Flash Player, even though you have installed the latest version.
- Some sites tell you to reinstall Flash Player, but after you do so, you see the same message.
Solutions:
The best solution is to use browsers like Google Chrome or Firefox for Flash Player if you have problems with Flash Player on Internet Explorer. But If you have problems with Flash Player on all browsers then keep reading.
First Solution:
Warning! By following the directions below, you will modify the Windows System Registry. A mistake could cause serious system damage, which may require you to reinstall your operating system.If you are not comfortable editing the registry, get help from your system administrator or another IT professional.
If you choose to proceed, first back up your entire hard drive, and create a Windows System Restore Point.
Adobe Systems cannot be held responsible for damage resulting from your following these instructions.
Note: The following solution is not required for Flash Player 10 and above. These registry changes were included in the Flash Player uninstaller and can be downloaded here.
- Make sure you are logged into a Windows Administrator account. If you are not, you will not be able to use SubInACL.
- Download SubInACL from the Microsoft Download Center.
- Follow the installation instructions. Make sure you install SubInACL (subinacl.exe) to the directory C:\Program Files\Windows Resource Kits\Tools.
- Download the reset_fp10.zip file.
- Open the fp10.zip file and extract the reset_fp10.cmd file to the directory C:\Program Files\Windows Resource Kits\Tools\.
Both this file and SubInACL (subinacl.exe) must be in this directory.
- Double-click reset_fp10.cmd. A command window will open, and SubInACL will run.
Do not use the machine while SubInACL is running.
- After SubInACL finishes, you will see a prompt “Press any key to continue”.
- Install Flash Player from the Flash Player download page.
- To confirm that your installation succeeded, visit the About Flash Player page. At the top of the screen, you should see a message that reads “Adobe Flash Player Successfully Installed.”
source: http://kb2.adobe.com/cps/494/cpsid_49419.html
Second solution:
For internet explorer:
1- Reset Internet Explorer settings:
- You can reset Internet Explorer settings automatically by downloading this tool from Microsoft: Reset Internet Explorer.
- You can reset Internet Explorer settings manually by following these steps:
A. Exit all programs, including Internet Explorer (if it is running).
B. If you use Windows XP, click Start, and then click Run. Type the following command in the Open box, and then press ENTER:
inetcpl.cpl
If you use Windows Vista, click Start

Type the following command in the Start Search box, and then press ENTER:
inetcpl.cpl
The Internet Options dialog box appears.
C. Click the Advanced tab.
D. Under Reset Internet Explorer settings, click Reset. Then click Reset again.
E. When Internet Explorer finishes resetting the settings, click Close in the Reset Internet Explorer Settings dialog box.
F. Start Internet Explorer again.
2- Install Adobe Flash Player manually:
Download the Flash Player from the Flash Player download page then follow the instructions to install the Flash Player.
source of resetting Internet Explorer settings : http://support.microsoft.com/kb/923737