Hi Enrique, which is your OS? I assume that you are using windows. Be sure that you follow the uninstall - install procedure.
From FAQ 3.3
We provide standard Windows installation packages. To install one of these packages, simply launch the executable file and follow the instructions. Once installed, you'll have a new PixInsight Platform entry on your Start > All Programs menu (Windows 7) or in the list of installed applications (Windows 8.), where you'll find an option or link to launch the PixInsight Core application. The installation also includes an uninstall utility.
Important: Under Windows, please uninstall a previous version, if you have one installed, before installing the latest package. For sanity, also reboot your machine after uninstalling the old version and before installing the new one. You must select the Uninstall option from the Start menu, under the PixInsight Platform item, or tell Windows to uninstall PixInsight. Never try to uninstall PixInsight by manually removing files.
See also the rest of FAQ 3.x that may also be useful.
Saludos, Alejandro.