How can I restore the default permissions to the NT structure?

Logon as administrator.

The built-in SYSTEM account needs access to the Windows NT default directories and subdirectories. To get this access, do the following:
- In File Manager use Security/Permissions to grant the SYSTEM account FULL CONTROL to the root directory of the NTFS volume that contains Windows NT.
- Next, select the option to Replace Permissions on Subdirectories, which gives SYSTEM access to the entire volume

Start Registry Editor (Regedit.exe).

Go to HKEY_LOCAL_MACHINESystemCurrentControlSetControlSessionManager

Double-click the value BootExecute.

Under BootExecute, you may find a few entries, such as:
autocheck autochk *
After any entries, add on a separate line:
setacl /a DosDevices:System32winperms.txt DosDevices:
Here is the drive that Windows NT is installed on and is the Windows NT root directory on that drive.

Save changes by clicking OK.

Exit the registry editor and restart the computer.

On restart, the system will set security on the system files to the norm

Logon as an Account that has "Backup files and folders" privilege

Run the FIXACLS.EXE utility (Start - run - fixacls)

Click the Continue button

Click OK when completed.

Start MMC.EXE

From the Console menu select Add/Remove snap-in

Add the Security Configuration and Analysis snap-in

Click Close then OK

Right click on the Security Configuration and Analysis root and select Open database

Enter a new database name and click OK

Select the 'basicwk.inf' template and click OK

Right click on the node again and select 'Configure Computer now'