How can I kill any task that takes up 50% of my CPU (or more) if using Windows Task Manager won’t kill it?
If you are on a "user" account then you can only kill processes which belong to your user(name).
If you are on an administrative account you should be able to kill any task.
Some tasks may be protected from a simple kill or may be "stubborn" enough not to get killed. In that case a third party tool might be able to help e.g. Process Explorer.
That being said DON NOT KILL tasks or processes just because they are using a lot of processing power. Take note of the process, search the internet for information, make sure the task is neither an important system component nor some malicious software your anti-virus didn't catch.
If you kill the wrong process you might end up crashing your system to a blue screen or worse, screw up your system to the point it won't boot up again!
which task it is?
you can try sysinternal process explorer
if you think is malware do a complete scan of your pc, with your antimalware tools, also with malwarebytes antimalware, superantispyware