http://helpx.adobe.com/flash-player/kb/flash-player-issues-windows-8.html

This page helps you to resolve issues that you can face while playing rich media content on embedded Adobe Flash Player on Windows 8.

Note: Flash Player is integrated with Internet Explorer in Windows 8. It’s unnecessary to install Flash Player.

Windows 8 provides Internet Explorer in two modes:

Windows Store mode: the version with a new appearance
Desktop mode: the version that’s more similar to the previous versions of Internet Explorer
Do the following if you find issues with playing rich media:

Check if the content can be played in the Desktop mode.
If content can’t be played in the Desktop mode:
Disable ActiveX Filtering
Enable Flash Player
Install the latest version of Flash Player
If content can be played in the Desktop mode:
Check the Compatibility View (CV) list
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From an expert: Installing Flash Player on Windows 8

Installing Flash Player on Windows 8

by Chris Campbell

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Check if the content can be played in the Desktop mode

If the content doesn’t play in the Windows Store mode, see if it plays in the Desktop mode by following the steps below:

Note: Flash Player is embedded in both versions. The Compatibility View (CV) list displays the list of non-compatible rich media content in Internet Explorer 10 in Windows Store mode.

If the content is not playing in Windows Store mode, it is possible that it is in the CV list. In this case, try to view your content in Internet Explorer in Desktop Mode.
Swipe from the bottom or top edge to reveal the application bar.

Open the Tools menu and select View On The Desktop. Check if you can view the content.

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Disable ActiveX Filtering

Open the page that has rich media content in Internet Explorer in the Desktop Mode. (See the previous section to know how to open the content in the Desktop mode.)

Select Tools > Safety. If ActiveX Filtering is selected, clear it.

Close the browser and open it. Then try to view the content.

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Enable Flash Player

Ensure that Flash Player is enabled.

Open the page that has rich media content in Internet Explorer in the Desktop Mode. For example, Find Flash Player. (See the previous section to know how to open the content in the Desktop mode.)

From the Settings menu, choose Manage Add-ons.

Select the Flash Player add-on: Shockwave Flash Object.

Note:
Make sure that the site has rich media content to see Flash Player in the add-on list.

Click Enable, and click then Close.

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Install the latest version of Flash Player

The content could require a later version of Flash Player than you have installed. See if you have installed the latest Flash Player version by visiting the Find Version document. The second step in the document displays the version of Flash Player that you have.

Flash Player is embedded in Internet Explorer in Windows Store and Desktop Mode. All updates are delivered through the Windows Update mechanism. You can also download and install the latest update from the following links:

64-bit machines
32-bit machines
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Check the Compatibility View (CV) list

Flash Player does not play content in the Windows Store mode if a website is listed in the Compatibility View list. Note that the CV list is managed and distributed by Microsoft.

Do the following to have the latest Compatibility View (CV) list:

Open the page that has rich media content in Internet Explorer in Desktop Mode. For example, Find Flash Player.

If the Tools menu is not visible in Internet Explorer, press and hold the title bar to open the context menu. (Or right-click the title bar.) Then, select the menu bar.

From the Tools menu, click Compatibility View Settings.

Select Download Updated Compatibility Lists From Microsoft, and then click Close.