In the same PC, using my account the program is not opening (just showing in the taskbar) but if I log in with different account the program is opening properly
If you see program in the taskbar then the application window is probably sitting somewhere outside of the screen (e.g. if you had dual monitor setup). The easiest way to fix it is to remove
.ganttproject file from your home folder (note the dot in the file name, it may be hidden in some file explorers). This file contains all settings, so make sure to back up it if you have anything valuable in he settings.