If Outlook does not open your data file, or you can not find some items in your inbox, contacts or calendar, then your PST is apparently corrupted. At this moment, thought about backup comes to your mind, but it is too late to muse about a backup. You need to backup your Outlook data in advance. Otherwise, you will need a repair tool.

If your data files in Outlook won't open, or items appear to be missing in your inbox, then your PST file is probably corrupted. However, there is a way to recover your emails, contacts, calendars, notes, etc.