Corrupted Dlls and exe's can be repaired by extraction from computer's operating system disk (supplied at purchase),  service packs  or a computer running the same operating system. Individual Microsoft files can be downloaded here. Security updates are available on ISO-9660 DVD5 image files from the Microsoft Download Center

To determine a dll's manufacturer, use Microsoft's Sigcheck utility.



Sigcheck run with -i option displays a file's catalog.



sigcheck -h -i ntdll.dll



Verified: Signed
Catalog: C:\Windows\system32\CatRoot\{F750E6C3-38EE-11D1-85E5-00C04FC295EE}\Package_25_for_KB948465~31bf3856ad364e35~x86~~6.0.1.18005.cat
Signers:
Microsoft Windows
Microsoft Windows Verification PCA
Microsoft Root Certificate Authority
Signing date: 7:38 AM 4/11/2009
Publisher: Microsoft Corporation
Description: NT Layer DLL
Product: Microsoft® Windows® Operating System
Version: 6.0.6001.18000
File version: 6.0.6001.18000 (longhorn_rtm.080118-1840)
MD5: 40db2eba3cd1433d1c90bd262ece1543
SHA1: 8618f3b335cc467574cc13cab11a798f0b46eb23
SHA256: e461850e92402912f022817ad66d715ed37b1ac6badf915316a761f0bcb2c7d8


visit Microsoft Update Catalog and type in the knowledge base number found in the above catalog field, KB948465 and download the update containing the dll or exe.

Re-register system dlls

For non Microsoft drivers, see Computer and device manufacturers

Device Drivers Id's

Device Driver List

Find a device driver: DriverAgent or DriverGuide

Video Drivers

Windows Hardware compatibility list