Er, that's not good if that file is missing, you're going to find quite a number of programs won't work if that's not there

You searched the whole Windows folder including subfolders? (Main subfolders to check are SYSTEM and SYSTEM32)

If it's not there, you'll have to restore it, either from wherever you installed Windows from, or reinstalling Windows back over itself. How you do this depends on the Windows version. What version of Windows are you using?


Other thing to do is check for viruses etc., that file shouldn't just disappear like that unless something is wrong with the computer.