What Operating System and which version of Zotero? Does it shut down after doing something specific?
Does it still shut down if you restart Zotero in Troubleshooting Mode (Help → "Restart in Troubleshooting Mode…”), which temporarily disables all plugins? Or if you cannot access the menus, hold down Option (Mac) or Shift (Windows) at Zotero startup to launch it in Troubleshooting Mode.
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Does it shut down after doing something specific?
Does it still shut down if you restart Zotero in Troubleshooting Mode (Help → "Restart in Troubleshooting Mode…”), which temporarily disables all plugins?
Or if you cannot access the menus, hold down Option (Mac) or Shift (Windows) at Zotero startup to launch it in Troubleshooting Mode.