Tommaso, this is an extract from Pixinsights system requirements document:
The only Windows platform supported officially by current versions of PixInsight is Windows 10.
Windows 7 and Windows 8/8.1 are no longer part of our mainstream supported platforms. We make efforts to ensure that PixInsight still can work on Windows 7 SP1 and Windows 8.1, but we no longer test the application on these Windows versions. This means that we cannot guarantee that current PixInsight versions will still work correctly on Windows 7 SP1 and Windows 8.1.
PixInsight 1.8.6 does not run on Windows Vista, XP, NT, 2000, ME, 98, 95, or 3.1x/Win32s.
Dave