How big is your mpp file? You may try increasing the amount of memory available
to Java Runtime. Unfortunately you can't do it for ganttproject.exe (which is
associated with GanttProject shortcuts in Windows menus) but you can do it for
ganttproject.bat which comes with ZIP distro (and with Windows distro too,
AFAIR). Try replacing -Xmx512m with -Xmx1024m in ganttproject.bat and start
that bat file.
Also I can suggest this program Recovery Toolbox for Project https://project.recoverytoolbox.com/
