Hi Graham,
What's the version of your Outlook and Windows system?
Please try the following steps to recover the Navigation Pane configuration file and see if there will be any improvement:
1. Press Win + R.
2. Type the following command in the search field:
outlook /resetnavpane
Note: Make sure to enter a space between outlook and /resetnavpane.
3. Press Enter and check if Outlook can be started as expected.
If the above method doesn't work, please try to repair the PST file using the Inbox Repair tool (SCANPST.EXE):
Repair a .pst file
Hope the above information can be helpful.
Best regards,
Yuki Sun
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