On rare occasions when working with Active Directory I find that the Active Directory Users and Computers control panel item is missing. I then have to open the Computer Management and have to wait for all of the various plug-ins to load in order to access the Active Directory Users and Computer plugin. An alternative to this process is to just run the command from the start menu:
%SystemRoot%\system32\dsa.msc
This method assumes that the Active Directory Users and Computers tool has not be uninstalled from that system. If you want to restore the missing control panel item, it might be best to simply reinstall the Active Director Users and Computers management tool. Don't reinstall AD, it is only the tool that you need.
We hope that this information is helpful. Please let us know how this has helped you or if you have additional questions. As always Firestone Technical Resources, Inc. is here to help with your computer support issues - "Providing personal service for your impersonal technology."