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Email & Outlook

"Cannot Start Microsoft Outlook. Cannot Open the Outlook Window"? Diagnose It in Order

Published June 10, 2026 · by The FixHub Team

Outlook won’t open: “Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened.”

Why /resetnavpane isn’t a cure-all: half the internet says “run outlook.exe /resetnavpane and you’re done.” That only fixes one specific cause (a corrupt navigation pane). This error has several causes, and applying the wrong step — like deleting the PST — can lose mail when the real problem was a bad add-in. Work through them in order, least-destructive first.

Fix 1: Start in Safe Mode to rule out an add-in

  1. Hold Ctrl while launching Outlook (or Win + R → outlook.exe /safe).
  2. If it opens in Safe Mode, a COM add-in is the culprit: File → Options → Add-ins → Manage: COM Add-ins → Go, untick add-ins, restart normally, and re-enable one at a time to find the bad one.

Fix 2: Reset the navigation pane (the genuine /resetnavpane case)

If Safe Mode opens fine but normal mode shows the error and the nav pane looks corrupt:

outlook.exe /resetnavpane

(Win + R, paste, Enter.) This rebuilds the nav pane XML. Only relevant to nav-pane corruption.

Fix 3: Repair or rebuild the data file

If it still won’t open:

  • Repair the OST/PST: close Outlook, run scanpst.exe (Inbox Repair Tool) against the data file shown in Control Panel → Mail → Data Files.
  • Rebuild an OST (Exchange/365): an OST is just a cache — close Outlook, rename the .ost to .old, reopen Outlook; it rebuilds from the server. (Don’t delete a PST this way — that’s your only copy.)

Fix 4: Create a new profile

If the profile itself is corrupt: Control Panel → Mail → Show Profiles → Add, set up the account, make it default. For Exchange/365 mail re-downloads; for POP, reuse the existing PST.

Fix 5: Repair Office

Settings → Installed apps → Microsoft 365 → Modify → Quick Repair (then Online Repair). Fixes a damaged Outlook install behind the error.

FAQ

Which fix should I try first? Safe Mode (Fix 1) — it instantly tells you whether it’s an add-in (most common) before you touch any data.

Is deleting the PST safe? No — a PST can be your only copy of that mail. Only the rename-to-rebuild trick is safe for an OST (Exchange cache). Repair a PST with scanpst instead of deleting.

Sources: Microsoft Support — “Cannot start Microsoft Outlook. Cannot open the Outlook window.”