Fix "The User Profile Service failed the logon" error using Regedit

Press the Windows key + R to open the Run dialog box.
Type “regedit” and press Enter to open Registry Editor. If prompted, click Yes to allow Registry Editor to make changes to your computer.
In Registry Editor, navigate to the following path: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
Under ProfileList, you should see a list of folders with long alphanumeric names. Each folder represents a user profile on your computer.
Look for the folder with the name that matches your affected user account. The folder name should end with “.bak”. For example, you should look for the folder named “S-1-5-21-xxxxxxxxxx-xxxxxxxxxx-xxxxxxxxxx-1001.bak”.
Right-click on the folder with the “.bak” suffix and select Rename. Remove the “.bak” suffix from the folder name. For example, rename “S-1-5-21-xxxxxxxxxx-xxxxxxxxxx-xxxxxxxxxx-1001.bak” to “S-1-5-21-xxxxxxxxxx-xxxxxxxxxx-xxxxxxxxxx-1001”.
Right-click on the folder without the “.bak” suffix and select Rename. Add “.bak” to the folder name. For example, rename “S-1-5-21-xxxxxxxxxx-xxxxxxxxxx-xxxxxxxxxx-1001” to “S-1-5-21-xxxxxxxxxx-xxxxxxxxxx-xxxxxxxxxx-1001.bak”.
Close Registry Editor and restart your computer.

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