How to Fix "The User Profile Service Failed the Sign-in. User Profile Cannot Be Loaded" (Registry Fix)

A corrupted user profile is one of the most common and disruptive issues on Windows 10 and Windows 11. When the User Profile Service (ProfSvc) fails to read the account's registry hive (NTUSER.DAT) or cannot establish exclusive lock on the user folder, Windows either halts at sign-in or automatically signs you into a temporary session (TEMP).

Symptoms & Diagnostic Observations

• Slow Sign-in: Windows sits on "Welcome" or "Preparing Windows" for several minutes before failing.

• Sign-in Error Screen: A modal dialog blocks sign-in stating: "The User Profile Service service failed the sign-in. User profile cannot be loaded."

• Temporary Profile Desktop: If sign-in succeeds, a desktop notification warns: "You have been signed in with a temporary profile." Desktop shortcuts, wallpapers, and files in Documents/Downloads appear missing.

Underlying Cause

During system shutdown or Windows Update, if an antivirus scan, background process, or sudden power failure interrupts profile unloading, Windows creates a backup key in the registry ending in .bak and attempts to boot from a blank fallback state. When Windows subsequently fails to mount the proper Security Identifier (SID), login is blocked.

The Solution: The Registry (.bak) Key Swap

This is the most reliable, non-destructive fix that restores your original profile without losing personal files or installed app settings.

Step 1: Access the Registry Editor

1. If you can log in with a secondary Administrator account or in Safe Mode, do so.

2. Press Win + R, type regedit, and press Enter.

3. Confirm the UAC prompt if requested.

Step 2: Locate ProfileList Entries

Navigate to the following key in the left panel:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList

Expand the ProfileList folder. You will see several sub-keys beginning with S-1-5-. Focus on the long keys ending in numbers like -1000, -1001, etc.

[Insert Guide Image Here: Registry Editor displaying the S-1-5... key and its matching .bak key]

Step 3: Perform the Key Swap

1. Look for two keys with the exact same SID number where one ends with .bak and the other does not:

   • S-1-5-21-...-1001 (Temporary/Broken key)

   • S-1-5-21-...-1001.bak (Original profile backup)

2. Click on each key and inspect the ProfileImagePath value on the right pane to verify it points to your actual username directory (e.g., C:\Users\YourUsername).

3. Right-click the key without .bak and rename it by adding .old to the end (e.g., ...-1001.old).

4. Right-click the key with .bak and remove the .bak suffix so it becomes the primary SID key (e.g., ...-1001).

Step 4: Reset State and RefCount Values

Select your newly renamed key (the one now without .bak):

1. In the right-hand panel, double-click State. Change its Value data to 0 (Hexadecimal) and click OK.

2. Double-click RefCount (if present). Change its Value data to 0 and click OK. (Note: If RefCount does not exist, you can leave it or create a DWORD (32-bit) with a value of 0).

Step 5: Restart the System

Close the Registry Editor and restart your computer. Log in with your original credentials. Windows will now attach to the original user hive, restoring your desktop, documents, and application configurations.