Windows Error 0xC004D401

Windows Error 0xC004D401

Windows now says:

“Windows Activation

An unauthorized change was made to Windows

You will no longer receive notifications, including those about your license or activation. Use the link below to find out how to fix your system.

Error: 0xC004D401

Description: The security processor reported a system file mismatch error.”

This error first comes up when I start the computer during the welcome screen or when I go on the internet and then go to Control-Panel and view Information about my system.

If it comes up during the welcome screen when I start my computer up, the welcome screen will remain there longer than usual and after a while this message pops up. All I can do now is close the error message. When I close the message windows logs me off and when I try to log back in the message will re-appear. Again when I close the message Windows logs me off. All I can do now is shut the computer down as the message will continue to come up and log me off.

If the error message comes up when I go to control panel and view system information this happens: If I am not on the internet it says that windows is activated however, when I go onto the internet and return to where it says “windows is activated” the error message pop-up and instead of saying “windows is activated” it says “This copy of windows is not activated. Click here to activate windows”.

When the error message comes-up when getting it through control panel the computer locks up, I cannot print or get onto control panel or well, do anything.

The only recent thing that I have installed onto the computer is Microsoft Silverlight, un-installing it has made no difference.

I have not modified my system in anyway, this message just first popped up when I started my computer today (3 March 2011).

I do not have any Virus’s etc. on my computer.

I have a perfectly legitimate version of Windows Vista SP1 Home Premium 64-bit.

All I have done so far to solve this is restart windows (several times) run some cleaning programs, and looked online for some help.

My computer has been running very smoothly for around 1 and a half years this has been my first major problem related to the OS.

I have also looked at a list of programs that may cause this problem and I do not have any of them.

System Spec’s (If you need them):

OS: Windows Vista SP1 Home Premium 64-bit

GPU: Nvidia Geforce GTX260 X2

CPU: Intel Core 2 Duo E7600 @ 3.06 GHz (2 CPU’s)


HD: 1GB Internal @ 5600 RPM


My Location: Australia, QLD, Brisbane.


Purpose of Computer: Gaming, Homework, Internet etc.


Could someone please help me fix this I have no idea how to fix this, everything I have tried has failed. Also I need this computer working ASAP, this is the main computer of the house and I have a lot of homework/assignments due soon.


My next 2 options that I can see is try doing a system repair (from the Windows Disk) or a complete Format of my hard drive and clean reinstall of Windows (Don’t really want to do this but If I have to I will).


As mentioned before I have a legitimate version of windows.


If someone has stolen my product key and done something to it (extremely unlikely) what can I do? Also if I do end up formatting is it almost certainly going to fix this problem?


I’m assuming something has happened to my windows and if I Format and do a clean reinstall of windows it will fix it.


Or is this something out of my control like Microsoft accidentally deactivating my product key or that someone has stolen my product key, because if I end up Formatting and doing a clean reinstall of everything this will have no effect. The message will still come up because my OS key has been compromised.


Please someone help me fix this as I’m a computer guy, (spend way too much time on my computer) and right now I’ve been freaking out for the past couple of hours (it will be very hard to sleep tonight).


Question Info

Last updated February 20, 2019 Views 14,597 Applies to:


1. click start, and in the Search box typeslui.exe 4 

2. press ENTER on your keyboard

3. select your country.

4. take the phone activation option, and hold on for a real person instead of following the automatic prompt process


·                        when you do the phone activation process hold on for a real person to explain to there instead of following prompts for automatic scenario





read below link on how to activate vista

How to activate Windows Vista


and if you have any problems doing it read information below

Keith-Support Engineer<abbr class="affil">Microsoft Support</abbr><abbr class="affil">, Moderator</abbr>






Windows can show as “Non-Genuine” for several reasons, such as incorrect Date and Time or an incorrect Product Key.


To verify Date and Time are correct:


·        Click the Start Button on the Desktop

·        In the Search field type Date and Time and press enter

·        Verify the date and time is set correctly


Retype the Product Key:


·        Click the Start Button on the Desktop

·        Select Computer

·        Select System Properties on the Taskbar

·        At the bottom click Change product key and retype your Product Key


Reactivate by Phone:


·        Click the Start Button on the Desktop

·        In the Search field type SLUI 4.exe and press enter (Note, there is a space between “I” and “4”)

·        Select your country

·        Call the phone number listed and follow the automated prompts.


If Windows is still showing Non-Genuine please download and run theMGA Diagnostic Tool, post the results along with any  previous troubleshooting steps performed in theMicrosoft Genuine Advantage forums.


Note: If your Operating System is Windows Vista SP1 or earlier you will notice you do not have access to the Start Button as Windows is in Reduced Functionality Mode.


If the Operating System is in Reduced Functionality Mode below are the steps needed to download and run the MGA Diagnostic Tool:


·        When you login to Vista, a window with several options will be available, select the option to open your  Internet browser.

·        Type: into the browser address bar.

·        A window will come up prompting to “Run” or “Save”, select “Run”

·        When the MGA Diagnostic Tool starts running click the “Continue” button, when the diagnostics is complete click the “Copy” button.

·        Paste the report into a thread in the appropriateWindows Genuine Advantage forum

Microsoft Answers Support Engineer
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