How to remove a corrupt SQL Server 2005 Express Instance?

The old Windows Installer Cleanup Utility download is retired. If Add/Remove Programs cannot remove the corrupt SQL Server instance, use Microsoft’s Program Install and Uninstall troubleshooter.
Remove the highlighted programs as shown in the picture.
Completely delete C:\Program Files\Microsoft SQL Server
Install using FR6 Installer
If instance error comes then remove the services.

How to Delete / Remove Services in Windows XP and Vista

Go to Start > Run > services.msc to start Services applet.
In the Services applet, find the service that you want to delete permanently, right click it and click on the Properties from the menu.
In the properties window, find the name of the service and copy it to your clipboard.
NOTE : ITS Service NAME / NOT the display Name.
You may also want to stop the service, if it is running; this will kill all the running processes for it.
Open a command prompt by going to Start > Run > CMD
Once a command prompt has opened up, type the command “sc delete service name” without the quotes, replace service name, with the name of the service you copied in above step.

Note : Once a service has been deleted you should see a message saying “[SC] DeleteService SUCCESS”, this should mean that the service has been deleted, to ensure that, just click on the refresh button in the services applet and confirm that the service has been deleted.

About installer cleanup tools

SUMMARY : When a program installation fails or a program cannot be removed cleanly, corrupted installer metadata may block the next install or uninstall attempt.

The old Windows Installer CleanUp Utility referenced in this legacy article is retired. Use Microsoft’s current Program Install and Uninstall troubleshooter for install/uninstall repair steps.