I think before we can answer the question, we need to know why you are
trying to delete dlls. What you are doing is dangerous. While some dlls
are installed by various applications, some are required by the system.
Just because an application was using a dll and the application was removed
does not necessarily mean all dlls used by the application should be
removed.
Generally, right clicking a file and selecting its properties will tell you
with what application it is associated. However, as mentioned, some such
dlls belong to the system and as such cannot be deleted.
I believe there are some third party applications that can tell you with
what applications a dll is associated but I'm not aware of anything that can
tell you specifically which application is using a specific dll. You might
want to make sure your antivirus application is up to date and do a virus
scan. You also should check for any malware on your system, download,
install and run Ad Aware:
www.lavasoftusa.com
The above will at least tell you if there's something else running on your
system that shouldn't. Also, instead of just looking at the application tab
in task manager, you should also look at the processes tab. Many such
processes you will recognize as perhaps being associated with some
application on your system. Others may be system related and any of them
might be running in the background. You should also check what runs when
you boot the system. Check the startup folder on the Start Menu, also from
start, type msconfig in the run box and press enter, go to the startup tab
and you will see a list of what is starting on bootup. Note, it is not
unusual to see more than one instance of svchost.exe in the task list, these
are usually system services but you should check viruses and malware as
mentioned above as they might attach to system services.
For an explanation of various services and what is necessary you might want
to check the following website:
www.blackviper.com