Removing malware from a PC can be a real problem, because the infection may try to counter everything you do: protecting its files, preventing you from launching antivirus tools, and more. But if that's happening, KillEmAll may be able to help.
Simply launch the program and it immediately tries to close all non-essential system processes. The program doesn't ask first, so be careful - if you have unsaved work open in a document somewhere, it'll probably be lost. Otherwise, though, if there is malware running then hopefully it will closed down along with everything else. And once this is done, an antivirus scan may stand a better chance of detecting and removing the threat.
There are no guarantees, of course. The malware may prevent KillEmAll from running. It might prevent itself from being closed down, or have another component which restarts it whenever necessary. But if you're manually malware-hunting then the program is a good place to start, and it includes several extra tools which you might find useful.
There are buttons to run a Google search on particular processes, for instance. You can upload them to VirusTotal to try and identify malware. If you're absolutely sure the file is dangerous, you can try to delete it, or there are a couple of "Rename" options if you're more cautious (you can always restore the file later, if it turns out to be innocent).
And if you find KillEmAll keeps closing some vital processes, then you're able to add them to a whitelist, and they'll be left alone.
On balance, this isn't a program you should take lightly. Closing multiple processes is dangerous, and there's no way of telling what might happen. Again, you get no warning of this - just launch KillEmAll and it leaps into action. And using the other tools to rename or delete executables can also cause plenty of problems; it's not something to try unless you're entirely sure what you're doing (and probably not even then).
But if you really are at the last resort - the regular antivirus tools have let you down, and a manual cleanup is the only option left - then KillEmAll is a very useful tool to have in your armoury. Go grab a copy for yourself (just don't run the program until it's needed).