DOCUMENT:Q174633  09-AUG-2001  [winnt]
TITLE   :Windows NT May Appear To Be Hung with Kernel Debugger
PRODUCT :Microsoft Windows NT
PROD/VER:WinNT:3.51,4.0
OPER/SYS:
KEYWORDS:

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The information in this article applies to:

 - Microsoft Windows NT Workstation versions 3.51, 4.0 
 - Microsoft Windows NT Server versions 3.51, 4.0 
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SUMMARY
=======

A computer running Windows NT version 3.51 or 4.0, appears to stop responding
(hang). There is no network connectivity to the computer, and there is no mouse
cursor movement or keyboard input.

CAUSE
=====

If the kernel-mode debugger is enabled on the affected computer, (the computer
is booted in debug mode) then the following could be causing the computer to
stop responding:

A DebugBreak function was called by a Win32 app and there is no user-mode
debugger specified on the computer. The int 3 will be reflected into the
kernel-mode debugger, causing the computer to appear like it has stopped
responding. Going to the computer's kernel debugger will show that the computer
is at a ntdll!DebugBreakPoint. Simply pressing "g" and Enter will release the
kernel debugger.

For more information on the kernel debugger, see the following Microsoft
Knowledge Base articles:

ARTICLE-ID: Q148954
TITLE : How to Set Up a Remote Debug Session Using a Modem

ARTICLE-ID: Q151981
TITLE : How to Set Up a Remote Debug Session Using a Null Modem Cable

For information on how to set up a user-mode debugger, see the following
Microsoft Knowledge Base article:

ARTICLE-ID: Q121434
TITLE : Specifying the Debugger for Unhandled User Mode Exceptions

MORE INFORMATION
================

When a Win32 user-mode application calls the DebugBreak function, the
application causes a breakpoint exception to occur in the current process so
that the calling thread can signal the debugger and force it to take action.

If there is no user-mode debugger specified to catch the int 3, and the
kernel-mode debugger is enabled on the computer, the int 3, will be reflected
into kernel-mode debugger and as a result, the computer appears to stop
responding.

Additional query words: debugref

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Keywords          :  
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT400search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS351search
Version           : WinNT:3.51,4.0
Hardware          : ALPHA PPC x86
Issue type        : kbprb

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