Why does my PC say the user profile Service failed the sign in?

Most Windows errors occur after you've logged on to your computer. But, the "The User Profile Service Failed the Logon" error doesn't let you sign in at all. That is why it is a bit trickier to resolve than other Windows errors.

However, you can use the following steps to diagnose and fix the issue effectively.

Boot Into Safe Mode

The first thing you should do is boot Windows into Safe Mode. While you cannot log in as you normally would, you can still use your computer in safe mode. Safe mode essentially boots Windows with the bare minimum features and programs that it needs to function.

To boot into Safe Mode, follow these steps:

From the Sign-In Screen

1. Power up your computer as you normally would.
2. When you reach the Sign In screen, hold down Shift and go to Power > Restart.
3. Your PC will boot into a blue screen with three options. Select Troubleshoot.
4. Click on Advanced Options > Startup Settings > Restart.
5. After your computer reboots, click on Safe Mode with Networking.
6. Your computer will restart in Safe Mode.

If You Are Unable to Reach the Sign In Screen

1. Hold down the Power button on your device till it switches off.
2. Press the Power button to start your computer. As soon as it switches on and you see the manufacturer's logo, press and hold the Power button again.
3. Repeat this process twice until your computer boots into the Windows Recovery Environment (winRE).
4. Now, follow steps 3, 4, and 5 from the section above.

Use SFC to Scan for Corrupt Files

The most likely cause for the "User Profile Service Failed the Logon" error is a corrupt user file. This can happen due to various reasons, ranging from antivirus software scanning upon boot to a power cut while powering on your computer.

Thankfully, Windows has some in-built utilities that can help you find and fix corrupt Windows files automatically. The utility is called System File Checker (SFC), and it is executed using Command Prompt:

1. Ensure that your computer is in Safe Mode.
2. In the Start menu search bar, type cmd and select Command Prompt.
3. In the Command Prompt window, type sfc /scannow and press Enter.
4. Windows will begin scanning your computer for any corrupt files and automatically fix them. The whole process should take about 30 minutes.
5. After the scan is complete, reboot your computer and try logging in again.

Restore Your Computer to an Earlier State

Windows has a useful feature called System Restore that lets you roll back changes to your computer and restore it to an earlier point in time.

Before proceeding further, you should know that the feature is not enabled by default, and you have to manually create restore points unless you use methods such as this one to create daily restore points.

If you remember creating a restore point before the error popped up, follow these steps:

1. Press Windows key + R to launch the Run dialog.
2. In the Run box, type rstrui.exe and hit Enter.
3. On the System Restore dialog box, click on Next.
4. Choose a restore point from the list.
5. On the next window, double-check everything and click Finish.
6. Windows will restore itself to an earlier state, and you should now be able to log in without any hassles.

You should back up any important data or applications that they may have installed after creating the restore point.

Change Registry Configuration

Another way to tackle the "User Profile Service Failed the Logon" error is to make some changes to the Registry. This is an advanced troubleshooting method, and it is recommended that you create a System Restore point before proceeding further.

Do the following to configure the Registry properly:

1. Boot into Safe Mode using the steps in the first section of this article.
2. Press Windows key + R to open the Run prompt. Type regedit and press Enter.
3. In the Registry Editor, using the navigation bar on the left, go to:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\Current Version\Profile List 

4. Here, you should see two files with the same name, but one will have .bak as an extension.
5. Right-click on the file with the .bak extension and select Rename. Remove the .bak extension while leaving the filename untouched, and press Enter.
6. Now, right-click on the file that didn't originally have the .bak extension and add .bak at the end of it.
7. In the folder that has the renamed file from step 5, right-click on State, then select Modify.
8. Change the value in Value data from 8000 to 0 (zero).
9. After this, right-click on the RefCount entry and change the value in Value data to 0 (zero).
10. Confirm the changes and close the Registry Editor.
11. Reboot your computer and log in.

What if You Don't Find a .bak File in the Registry Editor?

It is unlikely, but your computer may not have created a file with the .bak extension. In this case, open Windows Explorer and go to:

 C:\Users\Default\AppData\Local\Application Data\n 

If you find another folder named Application Data under the one you're on, delete it, and reboot your computer. It should fix the problem.

Enable the User Profile Service

In certain instances, the User Profile service itself may be disabled. Usually, a third-party application is the culprit. Luckily, you can enable it by running a simple command in the Command Prompt window:

1. Boot your computer into Safe Mode.
2. In the Start menu search bar, type cmd. From the search results, right-click on Command Prompt > Run as administrator.
3. In the Command Prompt window, type sc config ProfSvc start= auto and press Enter.
4. After this, type sc start ProfSvc, and press Enter.
5. Close Command Prompt and reboot your computer.

Log On and Use Your Computer

If you carefully followed the steps listed above, the "User Profile Service Failed the Logon" error should be a thing of the past.

Some of these methods are used to diagnose a lot of other common Windows errors as well. So, it's useful if you keep them in mind when you experience other issues on your computer.