That's the reason the software doesn't appear in the installed programs list. A manual transfer will simply copy the files, regardless if the software works or not. You will have to install the application properly, because when you do so, the installer will automatically add necessary information in the registry items.
A simple way to fix this is to export the registry file from the old computer. In case you still have access, go to Start > Run > regedit. Expand the Local_Machine > Software and export the folder associated with AutoCAD (most of the time it's called AutoDesk). Add it to the local PC and then try detecting the application again.
If this is not working for you, then reinstall the application using its own setup package.