This document provides steps to fix the Ntdll.dll error in Windows by reinstalling the .NET framework, downloading and replacing the missing Ntdll.dll file, re-registering the DLL file, enabling software rendering, replacing damaged installation discs, checking IDE cables, reinstalling Mathematica, unblocking Mathematica from DEP, deleting incompatible Acrobat plugins, and repairing the Adobe Acrobat installation.