The following software is known to crash MuseScore on startup:
MuseScore requires access to your internet connection with AVG. MuseScore doesn't need an internet connection to function, but if AVG blocks it, MuseScore hangs.
If AVG prompts you, Allow MuseScore and check "Save my answer as a permanent rule and do not ask me next time."
If it doesn't prompt you anymore,
MuseScore is known to display notes as square when some fonts are damaged on macOS.
To troubleshoot this issue:
In this forum article, a user believes to have found the font "Adobe Jenson Pro (ajenson)" to be the culprit, regardless of not being reported as broken, or problematic as per the above validation, and solved the problem by deleting that font, so this is worth checking too.
If the default desktop environment application font is set to bold, MuseScore will not display the notes properly.
To troubleshoot this issue (gnome 2.*/MATE users):
For GNOME 3/SHELL users
Some users reported that the Save As dialog is empty on Debian 6.0 and Lubuntu 10.10.
To troubleshoot this issue:
Type the following in a terminal
which mscore
The command will answer with the path of mscore. Edit it with your preferred text editor and add the following line at the beginning
export QT_NO_GLIB=1
Launch MuseScore and the problem should be solved.