How to Reinstall NTVDM.exe
The file "NTVDM.exe" is the Windows NT Virtual DOS Machine, which is responsible for running 16-bit tasks on 32-bit operating systems, including Microsoft Windows NT, 2000, XP, Vista and 7. It emulates MS-DOS to allow the programs based on it to run correctly. If the file becomes corrupted, most likely by a virus or malware, you may need to reinstall it by using the Windows XP installation CD.
Insert your Windows installation CD in the appropriate drive.
Open the search feature by clicking "Start" > "Search."
Specify the directory to search in by selecting your CD drive, which is "D:" by default. Search for "NTVDM.EX_," "NTVDMD.DL_" and "EXPAND.EXE" on the disk.
Copy the three files to your hard drive. Click "Start" and type "cmd" into the "Run" box. Click "OK."
Type "expand ntvdm.ex_ ntvdm.exe" into the command prompt and press "Enter." Type "expand ntvdmd.dl_ ntvdmd.dll" and press "Enter." Close the command prompt.
Copy the expanded files into the "C:\Windows\System32" folder. If Windows prompts you to replace the current files, click "Yes."