Sometimes you might have to re-install the SharePoint binaries again on the server trying to fix some corruption.

When you click on the uninstall or change button in the Add/Remove program, you get error message like :

“This product installation has been corrupted.  Run setup again from the CD, DVD, or other original installation source.”

Before you begin the manual uninstall procedure, ensure that you have taken a working backup of the databases and the farm and that you disconnect the SharePoint server from the existing farm either by:

>> Running the “SharePoint Products and Technologies Configuration Wizard” and disconnecting the SharePoint server OR
>> By running the following command:  psconfig –cmd configdb -disconnect

Steps to uninstall SharePoint 2007
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- Disable and Stop the following services: 
    Microsoft Single Sign-on Service
    Windows SharePoint Services Administration
    Office SharePoint Server Search
    Windows SharePoint Services Search
    Windows SharePoint Services Timer
    Windows SharePoint Services Tracing
    Windows SharePoint Services VSS Writer


-  Note the following registry keys:
From HKLM\Software\Microsoft\Office Server\12.0
    InstallPath (default is C:\Program Files\Microsoft Office Servers\12)

From HKLM\Software\Microsoft\Shared Tools\Web Server Extensions\12.0
    Location  (default is C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12)

- Take a Registry hive backup and then delete the following registry hives:

    HKLM\Software\Microsoft\Office Server\12.0
    HKLM\Software\Microsoft\Shared Tools\Web Server Extensions\12.0
    [x32] - HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall\OSERVER
    [x64] - HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\OSERVER

- Then delete the following folders:
    The value of the InstallPath key
    The value of the Location key

- If you are unable to delete the folder, due to any dll /file in used / locked , you can either reboot the server or use Process Explorer tool  
   http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx

- After Deleting the above folders successfully, Uninstall SharePoint using Windows Installer Cleanup utility:
   Download the tool from http://support.microsoft.com/kb/290301

- Select the entries that start with
“Microsoft Office SharePoint *.*” ,“Microsoft SharePoint Service *.*” and “Microsoft.Office*.*” having the same binaries version as the Server and select remove.

NOTE:

If you have any other Microsoft Office product (like Project server, PerformancePoint) installed on the server, you will find these Products also to remove. Carefully select ONLY the ones having the same binaries version as the SharePoint Server and not the other ones.

- You can run the binaries again and ensure that it is successfully, now you can again try to do a clean uninstall from the Add/Remove program and in supported state.

Hope this helps.