Installation & Licensing
To Diagnose and Fix installation problems automatically, please see the new Microsoft tool for this here:
http://support.microsoft.com/mats/Program_Install_
For more information on the Autodesk KB Support article concerning the clean uninstall of Autodesk products, see this link:
http://usa.autodesk.com/adsk/servlet/ps/dl/item?si
For all other installation problems consider using the Microsoft Installer Clean Up Utility. For more information on this program, please my forum post here:
http://forums.autodesk.com/t5/Installation-Licensi
If my post was helpful, please give 
Hello. What exactly says this is installed on your computer? Is it the download manager saying it is downloaded or do you run the installer and it says it is installed?
Is it installed in the Control Panel Programs and Features list?
Do you just not have desktop icons? Is it available in the Windows start menu program list?
Do you have install folders in your C:\Program Files\folder?
IF you are running the installer and the installer says the program is already installed, and you checked the Control Panel and folders and start menu and are sure that it is not installed- you likely have a rouge entry key for AutoCAD.
Okay, you will find Autodesk products are listed in groups of 2. One for the base program and one for a language pack. You should only need to delete these two keys (for one product) and when you highlight the key on the left of the reg window, the name of the program will display on the Right pane clearly. If it does not have your product name you selected the wrong key.
The install keys you are looking for are in this registry folder:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Prod
The actual key will have a numeric/character combo neither of us understand. If you select the various keys, you will see various products display on the right pane.
So… you should probably backup your registry at this stage. Then...
1.) Click the Windows Start Button
2.) Type Regedit in the run box and press [Enter] to open the registry editor
3.) Look for the AutoCAD 2013 keys
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Prod
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Prod
4.) Note that when you select the key on the left, you can see the product name on the right grouping of data.
5.) Delete these two keys and you should be able to install AutoCAD 2013.
If you are talking about a different product, this is the area the keys will be:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Prod
Find your product keys and remove them.
Thank you for taking part in our community!
David Dembkoski
Product Support Specialist
Autodesk Product Support
