Google translate: "I have a problem associated with installing AutoCad in the student version. I install it on my computer and when the "Configure Installation" screen appears, it states that the application is already installed on my computer, but it is not. I need AutoCAD for college projects."
Use the Microsoft uninstall tool to remove the corrupt install/traces of the previous installation, clear our your temporary files folder, then try again. If you were using "Install Now" method originally, try the "Browser Download" instead.