why is Pro XI freezes immediately when opening file?

I am suddenly experiencing a similar problem in Acrobat XI Standard - after flawless operation for the last 10 months.   Nothing has changed in my Adobe setup.

I have tried to reset preferences but this does not seem to work.  I completely uninstalled Adobe XI Standard this afternoon and reinstalled.  This worked for a few hours but now it's back to freezing.
I open up a PDF file but it freezes when I try to scroll or change pages - Adobe Acrobat (Not Responding).

Eventually - after it blanks out - a dialog box asks me to wait, or close.  The Problem Details Box shows the following:

Description:

  A problem caused this program to stop interacting with Windows.

Problem signature:

  Problem Event Name: AppHangB1

  Application Name: Acrobat.exe

  Application Version: 11.0.14.16

  Application Timestamp: 56731fe8

  Hang Signature: c90f

  Hang Type: 0

  OS Version: 6.1.7601.2.1.0.256.48

  Locale ID: 4105

  Additional Hang Signature 1: c90fa88b0dee4129c8afb0793a69a1e8

  Additional Hang Signature 2: db17

  Additional Hang Signature 3: db17a04f899f5b0c9f3091ce7cc85a3d

  Additional Hang Signature 4: c90f

  Additional Hang Signature 5: c90fa88b0dee4129c8afb0793a69a1e8

  Additional Hang Signature 6: db17

  Additional Hang Signature 7: db17a04f899f5b0c9f3091ce7cc85a3d

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Very frustrating!!!
Looking for help.

Thanks,
Herb...