How to overcome Access Denied when killing process in Windows?
Depending on the state of the process, there may be no way to kill it at all. See this answer for a more detailed discussion, the crux of which is:
If it doesn't go away, it's currently locked waiting on some kernel resource (probably a buggy driver) and there is nothing (short of a reboot) you could do to make the process go away.
Check this Wikipedia section:
The purpose of the administrator account is to allow making system-wide changes to the computer (with the exception of privileges limited to Local System)
As the Adminstrator, you're (close to) the boss of user space (apart from the above caveat about Local System). The buggy driver is running in kernel mode. See Jeff Atwood's writeup on the two modes here.
Process Hacker utility will do this for You for Your own risk, of course, because killing system processes is sometimes risky!
I can confirm all these "unable to kill the application, access denied" problems are related to faulty drivers.
I had that problem in Windows 8.1 for quite some time, it was driving me nuts until I discovered it was one of my USB MIDI controllers.
So..! the best way to solve this is:
you get the stuck app, it says "access denied" when you try to kill it.
Open your task manager.
Start disconnecting devices while looking carefully at the task manager.
Once you unplug something and the app goes away from the task manager you KNOW it is causing the problem.
Update the driver or wait for a new one for the offending device.