Adobe flash will not load - gives only a black screen

Question

For all the (3) users on this computer.   For most browsers (Safari, Chrome, Firefox) The browser window goes 100% BLACK when a flash program link is opened and most of the time the cursor / Pointer freezes (occasionally disappears and all keyboard actions are blocked.  Have to force quit or kill the box with the power key (which always bothers me.)  No Adobe links work directly via the link in mail or in browser.  Symptom in Mail is either the original window goes BLACK or a separate window opens in Black.
Current OS X 10.9.3 (13D65), Memory 4GB on 2.4 GHz Intel core i7 in MacBook Pro  15" Late 2011.
Relevant?? Items:
1.     The Adobe company checking device says Flash is not loaded.  I have had flash 9, 10, 11, 12, & 13 working before the latest of   OS X upgrades were made.
2.     An aside, I recently (4 months ago) used a MacKeeper app.  Today (not used except for information gathering) the "System Scan says my ProtectMac anti-virus is active and no security problems noted.  Also noted was "Serious" issue relating to one of 128 issues (474.3 MB of 'junk' files-36.9 MB in 'Logs", 437.4 MB in Caches.)  "Performance" listed as 'Fast.'  No action is taken and System Scan app closed.
3.     I seem to have lost my copy of Flash 13 in the Applications folder and the install file tries to load  "AdobeFlashPlayerInstaller_14_ltrosxd_aaa_aih.dmg"
This makes sense as to item 1. above. 
4.      Another user loaded adobe flash 11 from a download file called, "AdobeFlashPlayerInstaller_11au_ltrosxd_aaa_aih.dmg."  I do not understand the meaning of  the part of the file name that reads "_11au_" as it seem to differ from other downloads for "_11eu_".  Additionally the copy retained is filed in history and had only the user permissions of one user.  Also that copy _11au_ has no mention of Browser Type in the name description of the .dmg file; but the "_11eu_" does mention Safari browser.   Since it was from July 8, 2013 I assume it doesn't matter and it should have been superseded by Flash 12 OSX.  Mentioned here only for interest.  Also, It may have been saved on this computer in case of rebuild for another user on the home network running 13" MacBook Pro 10.6 Leopard.
5.  Attempts to reload Flash 13 from 'AdobeFlashPlayerInstaller_13au_ltrosxd_aaa_aih.dmg' as the "Adobe Flash Player Installer" connects to the latest version not yet installed and keeps downloading the Flash 14, which fails and locks up the browser.
6.     The download from get,Adobe.com starts out O.K.  After the installer file.dmg completes well, Step 2. is to open it, that, too, works well with an open window of a mounted device on the desktop.  The next step is to double-click the icon.  That only works so far.  A window opens and it has a progress thermometer but it never downloads any product and the link is declared "unavailable" immediately.  Refuses to load and will not always give the pointer back or let the browser continue.
7.     While creating this 'Summary' something changed.  Using Spotlight I found a different version of Flash Installer on my Mac.  I clicked it to go to the Black screen after installer download competes and got a totally different response.  I was set to take snapshots of the windows as they progressed.  The ".dmg" Icon on the desktop changed from default plain white disk to the red "Flash Player" I had not seen for last 40 days. 
Pic 1.     Pic 2.   
Pic 1. is the desktop device icon.
Pic 2. is the Installer.
Pic 3. is the Acceptance popup.  ~~Note: This popup shows a backwards rev dated March 4, 2012!  today is 10 July, 2014.
Flash Player 11.6 is installing after acceptance of License.
Everything went normally and loaded but I cannot test it as all browsers were closed. 

Answer 1

Please read this whole message before doing anything.
This procedure is a test, not a solution. Don’t be disappointed when you find that nothing has changed after you complete it.
Step 1
The purpose of this step is to determine whether the problem is localized to your user account.
Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”
While logged in as Guest, you won’t have access to any of your documents or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this behavior; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
Test while logged in as Guest. Same problem?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.
*Note: If you’ve activated “Find My Mac” or FileVault, then you can’t enable the Guest account. The “Guest User” login created by “Find My Mac” is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.
Step 2
The purpose of this step is to determine whether the problem is caused by third-party system modifications that load automatically at startup or login, by a peripheral device, by a font conflict, or by corruption of the file system or of certain system caches.
Please take this step regardless of the results of Step 1.
Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem. You must hold down the shift key twice: once when you turn on the computer, and again when you log in.
Note: If FileVault is enabled, or if a firmware password is set, or if the startup volume is a Fusion Drive or a software RAID, you can’t do this. Ask for further instructions.
Safe mode is much slower to start up and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal startup may also be somewhat slow.
The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
Test while in safe mode. Same problem?
After testing, restart as usual (not in safe mode) and verify that you still have the problem. Post the results of Steps 1 and 2.