Do the following to restore all your system files back to default:

  1. Press Control + Shift + Escape. The Task Manager will open.

  2. Click File -> Run new task.

  3. Click Browse.

  4. Type %windir%\system32 in the File name: textbox and press Enter.

  5. Right-click cmd.exe and click Run as administrator.

  6. Type sfc /scannow in the window that appears and press Enter.

  7. Restart.