Microsoft Outlook app not opening on your Windows machine? Try this

Microsoft Outlook is refusing to open for a growing number of Windows users, and it’s been causing headaches since around December 5. If you’ve tried clicking the app icon only to watch nothing happen, you’re not alone.

Users have taken to Reddit’s r/Outlook subreddit to complain about the problem, noting that the desktop app is completely failing to launch on both Windows 10 and Windows 11 machines. The usual troubleshooting steps — safe mode, resets, even full uninstalls and reinstalls — did absolutely nothing.

One user spotted error code 0xc0000409 in Windows Event Viewer logs, pointing to a crash involving OUTLOOK.EXE, but Microsoft hasn’t publicly acknowledged the problem yet.

The good news? Reddit user Annual-Volume3978 posted a surprisingly simple fix that’s been working for affected users.

Here’s what you need to do: Press Windows Key + R to open the Run dialog, then type %localappdata%\Microsoft and hit Enter. Once you’re in that folder, delete both the Olk and OneAuth subfolders. Restart Outlook, and it should open normally.

Multiple users confirmed the workaround in the Reddit thread, with responses like “This worked, not sure how you figured it out” and “You are an angel, thank you!” flooding the comment section. It’s worth noting that some users reported their Outlook interface looked different after applying the fix, though functionality returned to normal after removing and re-adding email accounts.

This appears to be a server-side issue or a bad update from Microsoft’s end. The fact that traditional repair methods failed suggests something broke on Microsoft’s side rather than individual user configurations being corrupted.

For now, the fix seems stable for most users. If Microsoft pushes out an official patch or acknowledgment, we’ll update accordingly, but until then, this community-sourced solution is your best bet for getting back to your inbox.