You double-click Outlook and the splash screen stops on one line and stays there:
Outlook
Loading Profile...Sometimes it says Processing instead, or the window goes white with “Not Responding” in the title bar. Waiting longer does not help. The usual triggers are a crash or forced shutdown, a Windows or Office update, or a new add-in. This article takes the causes in order, from the cheapest and safest fix to the most destructive, and tells you what to check before you touch a data file.
Applies to: classic Outlook for Windows (the one with a File menu and a ribbon, from Microsoft 365 Apps, Outlook 2021 or 2024). The new Outlook does not use Outlook profiles, so none of this applies to it. Everything below can be done as a normal user unless a step says otherwise.
What is going on
Before the Inbox appears, classic Outlook has to load your profile (the saved list of accounts and data files), start each add-in, and open the local data files. An Exchange or Microsoft 365 mailbox keeps a cached copy in an .ost file. POP accounts, and anything you archived, live in a .pst file. If any one of those steps waits on something that never answers, the splash screen just keeps saying “Loading Profile”. The usual suspects are an add-in that is waiting on a sign-in, a data file that is damaged or locked, a leftover Outlook process from the last session, or a bug in a recent Windows update.
That is why the order matters. Ending a stuck process and trying safe mode cost nothing and change nothing. Rebuilding an OST or creating a profile means a long re-download, and doing it to the wrong kind of account can lose mail.
Diagnosis
1. Make sure no old Outlook is still running
A previous Outlook that never finished closing can hold the data files open, so the new one waits forever. Press Ctrl+Shift+Esc to open Task Manager, find Microsoft Outlook (or OUTLOOK.EXE on the Details tab), and choose End task. Or from PowerShell:
Get-Process OUTLOOK -ErrorAction SilentlyContinue | Select-Object Id, StartTime, Responding
Stop-Process -Name OUTLOOK -Force -ErrorAction SilentlyContinueWait a minute, then start Outlook once. If it opens, you are done; if it was already open before this step and keeps doing it, carry on.
2. Check Windows Update first
Microsoft documented a known problem after the Windows 11 update KB5074109 (13 January 2026): classic Outlook profiles that use POP accounts or PST files hung, showed “Not Responding”, and could not be reopened without ending the process. Microsoft’s support article says the issue has been fixed by Windows and that you get the fix by running Windows Update until it says You’re up to date. Its interim advice was to use webmail and to move PST files out of OneDrive. If your profile uses POP or a PST file and the hang started after an update, do this before anything else, then restart.
Not on a managed PC? Settings > Windows Update > Check for updates, repeat until nothing is offered, then restart. On a managed PC, ask your IT team before uninstalling any update.
3. Start in safe mode
Safe mode starts Outlook without add-ins and with customisations switched off. Press Win+R and run:
outlook.exe /safePick your profile if it asks. Type the command exactly, with a space before the slash. The result tells you where to look next:
- Safe mode opens fine: an add-in or a customisation is the cause. Go to step 4.
- Safe mode hangs on Loading Profile as well: add-ins are ruled out. The profile, a data file, or the Office install is the problem. Go to step 5.
4. Find the add-in
In safe mode, open File > Options > Add-ins. At the bottom, set Manage to COM Add-ins and select Go. Untick everything that is not from Microsoft (PDF tools, CRM and conferencing add-ins, antivirus plug-ins), select OK, close Outlook, and start it normally. If it opens, turn the add-ins back on one at a time, restarting each time, until it hangs again. That is your culprit: update it, or leave it off.
Microsoft also lists File > Slow and Disabled COM Add-ins, where Outlook shows add-ins it has already switched off for being slow. An add-in you once forced back on with “Always enable this add-in” can be switched off again there.
If the Inbox opens but the folder list looks wrong or empty, outlook.exe /resetnavpane clears the navigation pane customisations and is harmless to try.
5. Look at the profile before changing it
Once safe mode has ruled add-ins out, find out what the profile actually holds, because the next steps depend on it. Open Control Panel, search for Mail (Microsoft Outlook), then choose Email Accounts and look at the Data Files tab. You can also list the usual folder from PowerShell:
Get-ChildItem "$env:LOCALAPPDATA\Microsoft\Outlook" -Include *.ost,*.pst -Recurse -ErrorAction SilentlyContinue |
Select-Object FullName, @{n="SizeGB";e={[math]::Round($_.Length/1GB,2)}}, LastWriteTimePST files are often kept elsewhere (for example Documents\Outlook Files), so trust the Data Files tab over the folder listing. Write down the answers to three questions:
- Is the mailbox Exchange or Microsoft 365? The .ost is only a cache of the server copy, so it can be rebuilt.
- Is any account POP, or is there a .pst the profile opens? That file may hold the only copy of the mail.
- Does a .pst live inside OneDrive or another synced folder? Microsoft’s advice is to move it out; sync tools and open PST files do not mix.
6. Repair Office
Repairing Office does not touch your mail or profile, so it is a reasonable, low-risk step once add-ins and Windows Update are out of the way. Go to Settings > Apps > Installed apps, find Microsoft 365 (or Microsoft Office), open the … menu, choose Modify, and run Quick Repair first. It works offline and takes a few minutes. Online Repair reinstalls Office from the internet; it is slower and needs a good connection, so save it for when Quick Repair has not helped. Neither should be needed more than once.
Root cause
There is no single cause, which is why the steps are ordered rather than prescribed. In practice it is one of: a leftover Outlook process holding the data files, a recent Windows update bug (POP and PST profiles, January 2026), an add-in stuck during start-up, a damaged or locked data file, or a damaged profile. Safe mode and the Data Files tab tell you which of these you are dealing with.
The fix
Back up before the last two steps. Copy any .pst file you find to another drive or folder (not OneDrive) while Outlook is closed. Never delete a PST. It can be the only copy of that mail. The steps below only ever rename a file, so you can undo them.
A. Rebuild the OST (Exchange or Microsoft 365 mailboxes only)
An OST is a cache. If it is damaged, Microsoft’s documented fix is to remove it and let Outlook download everything again from the server. Close Outlook completely first (step 1), then rename the file for your address rather than deleting it:
$ost = Get-ChildItem "$env:LOCALAPPDATA\Microsoft\Outlook" -Filter *.ost
$ost | Select-Object Name, Length, LastWriteTime
# Rename the one that matches your mailbox (replace the name)
Rename-Item "$env:LOCALAPPDATA\Microsoft\Outlook\you@example.com.ost" "you@example.com.ost.old"Start Outlook. It shows a “preparing for first use” style message and then re-synchronises; a large mailbox can take hours to finish, though the Inbox is usable sooner. Delete the .old file only once everything looks right.
When not to do this: if the profile uses POP, or only a .pst, there is nothing on a server to download again. The same goes for local-only items such as an On My Computer folder or a local calendar. Microsoft’s guidance for the rare case of items that exist only in the OST is to export them to a PST first. For an IMAP account, the OST is a cache of the server too, but export first if you are not sure everything was synced. If a PST is damaged, copy it, then run Microsoft’s Inbox Repair Tool (scanpst.exe) on the copy.
B. Create a new profile (last resort)
Open Control Panel > Mail (Microsoft Outlook) > Show Profiles > Add. Name it, add your account, and select Always use this profile. Do not remove the old profile yet. Microsoft warns that removing a profile deletes the offline cached content that belongs to it, so only delete the old one when the new one has been working for a few days and any PST has been re-attached (File > Open & Export > Open Outlook Data File).
Verification
Start Outlook from the normal Start menu or taskbar shortcut, not from the Run box. It should get past “Loading Profile” in seconds and show the Inbox. Then check three things: new mail arrives, a message you send goes out, and File > Account Settings > Data Files lists the PST files you expect. Restart your PC once and open Outlook again; a fix that only works until the next reboot is not a fix.
Notes
- Do not reinstall Windows. Nothing in this problem calls for it.
- Quick Repair is cheap, so it is not a wrong turn. It just rarely helps with a hang that safe mode already narrowed down to an add-in or a data file.
- Hangs that come back every few weeks usually point at a single add-in, a PST in OneDrive, or an unfinished Windows update. Fix that, not just the symptom.
- If a security product on the PC includes an Outlook add-in or email scanning, that is also an add-in as far as Outlook is concerned. Microsoft notes antivirus Outlook integration can cause Outlook to freeze; disable the integration, not the antivirus.
- For several PCs at once, look at what changed centrally (a Windows update, an Office update, a new add-in deployed by policy) before touching any single profile.
Still stuck? Tell us in The Patch Panel whether safe mode opens, what the Data Files tab lists (file types only, no names) and which Windows updates were installed just before it started, and we will work through it. The best answer earns points on Top of the Stack.