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.