A file named NTUSER.DAT is hidden in each user profile. This file contains the settings and preferences of each user. Therefore, you must not delete or modify it. Windows automatically loads, modifies and saves the file for you.
NTUSER.DAT contains your user profile settings
Whenever you change the appearance and behavior of Windows and installed programs, whether it is your desktop background, the resolution of your monitor, or the default printer, Windows should keep your preferences when it's next loaded.
Windows accomplishes this by first storing this information in the register in the HKEY_CURRENT_USER hive. Then, when you log off or close the computer, Windows saves this information in the NTUSER.DAT file. The next time you log in, Windows will load NTUSER.DAT into memory and all your preferences will be loaded back into the registry. This process allows you to define personal settings that are specific to your user profile, such as the background of your choice.
The name NTUSER.DAT is a Windows NT retention, first introduced with Windows 3.1. Microsoft uses the DAT extension with any file containing data.
Each user has a NTUSER.DAT file
Windows was not always fully compatible with user profiles. In early versions when you started Windows, each computer user saw the same desktop, the same files, and the same programs. Now, Windows better supports multiple users on the same computer by placing a NTUSER.DAT file in each user's profile. You can do this by opening File Explorer and navigating until:
C: Users * YourUserName *
or by typing:
% user profile%
in the address bar of the File Explorer, and then pressing Enter.
If you do not see NTUSER.DAT yet, do not worry. Microsoft does not intend to allow you to modify or delete this file. Therefore, they hide it. You can turn on the Show hidden files possibility to make the file visible.
You will probably notice that in addition to a NTUSER.DAT file, there is also one or more ntuser.dat.LOG files. Whenever you make a change, Windows saves your new preferences in the NTUSER.DAT file. But first, it creates a copy and renames it to ntuser.dat.LOG (plus an incremented number) to save your previous settings. Even Microsoft knows that you should always back up your settings and files.
Do not delete the NTUSER.DAT file
You should never delete your NTUSER.DAT file. Because Windows depends on loading your settings and preferences, removing it may corrupt your user profile. The next time you log in, you will see a prompt stating that Windows can not log in to your account.
Despite the suggestion that disconnecting and then reconnecting can solve the problem, the same message will reappear. If you try to create a simple NTUSER.DAT file to replace the missing instance, you will encounter a loop in the first installation dialog and Windows will never complete the connection.
The NTUSER.DAT file is usually not a large file, ranging from 3 megabytes on one of our new computers to 17 megabytes on a PC we have been using for a few years. Deleting it will not usually recover much space, but the results may be disastrous. If a user profile is not needed, it's better delete the user account through Windows.
You probably should not change it either. Some administrators can do this to make quick changes to many users, but if you're not careful, you can cause hard-to-solve problems.
The best thing to do is use regedit make changes to the registry. Working in the registry is also something to do with caution, but it is likely that you will find a guide that will guide you through the necessary steps. After changing the registry on your next close or close, your new settings will be saved to the NTUSER.DAT file.