Why can't I install Adobe Flash Player on my mac?

Without knowing the OSX version you are using maybe this will help

How to perform a "clean install" of Flash Player in Mac OS X

If you can't install or update Flash, follow these instructions.

If you have installed the latest version of Flash, please take each of the following steps that you haven't already tried. After each step, relaunch Safari and test. For a "missing plug-in" error, start with Step 8. Back up all data before making any changes.

Step 1

You might have to log out or restart the computer before a Flash update takes effect.

Step 2

From the Safari menu bar, select

Safari ▹ Preferences... ▹ Privacy ▹ Remove All Website Data...

and confirm. Close the window. Then select

 ▹ System Preferences… ▹ Flash Player ▹ Advanced

and click Delete All. Close the preference pane.

Step 3

If you're only having trouble with YouTube videos, log in to YouTube and load this page. You may see a link with the text "Leave the HTML5 Trial." If so, click that link.

Step 4

a. If you get a warning of a "blocked" or "outdated" plug-in, then select the Security tab in the Safari preferences window. In the list of plugins on the left, there should be one—and only one—entry for "Adobe Flash Player," showing the same version number that you installed. Select that entry. On the right there will be a list of websites for which you have specifically allowed Flash, if any. It's normal for the list to be empty. Below that is a menu labeled

When visiting other websites

From that menu, select either Allow or Ask.

b. If you still get the alerts, then go back to the Flash Player preference pane and select the Advanced tab. Click Check Now. Quit and relaunch the browser.

c. If the alerts still persist, triple-click anywhere in the line below on this page to select it:

/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources

Right-click or control-click the highlighted text and select

Services ▹ Open

from the contextual menu.* A folder should open. Inside it, there should be a file named "XProtect.meta.plist". If that file is missing and you know why it's missing, restore it from a backup or copy it from another Mac running the same version of OS X. Otherwise, reinstall OS X.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select

Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.

Step 5

In the Safari preferences window, select the Advanced tab and uncheck the box marked

Stop plug-ins to save power

Step 6

Open this folder as in Step 4:

/Library/Internet Plug-Ins

Delete the following item, or anything with a similar name, if present:

Flash Player (failing).plugin

You may be prompted for your login password.

Step 7

Re-download and reinstall Flash. Download it from the domain "get.adobe.com". Don't click a link from any other website, including this one, because you can't trust links. They may be an attempt to trick you into installing malware masquerading as Flash. Type the address into the browser window. Never download a Flash update from anywhere else.

Step 8

If you get a "missing plug-in" error, select

Safari ▹ Preferences... ▹ Security

from the Safari menu bar and check the box marked

Allow (or Enable) plug-ins

Then click the button marked

Manage Website Settings...

if present and make sure that the website is not blocked for Flash.

Step 9

Select

Safari ▹ Preferences... ▹ Extensions

from the Safari menu bar. If any extensions are installed, disable them.