There is a Windows XP machine whose CPU usage is continuously at 100%.
When watching processes in the Task Manager (sorted by CPU usage), the percentage does not add up to a 100%.
This points to a virus or some other kind of rogue process.
There is an antivirus (Kaspersky) running on that machine and has been run but doesn't detect anything.
So, even if it might be saner and shorter to just reinstall, what does your toolkit contain to find the culprit and handle this type of scenario?