My mother’s laptop has been behaving very strangely lately. CPU usage suddenly would spike to 100% usage inexplicably. It seemed to happen more often when Firefox / Thunderbird were launched, but that wasn’t necessarily the case. The issue would often persist across reboots.
My first thought, of course, was malware. An extensive scan via rootkit scanner, malware scanner, spyware scanner, and anti-virus revealed nothing. Observing running processes with process explorer and startup programs with autoruns revealed nothing suspicious. I installed all Windows updates, updated all typical applications with the help of ninite, and even ran sfc /scannow for good measure. The issue remained!
Even more confusing is that when running task manager, process explorer, or performance monitor they all reported 100% CPU usage and with a single process hogging the CPU – themselves! It seemed that whatever was the last process to execute was taking all CPU. It was truly baffling.
A suggestion on superuser.com was to remove the laptop battery and try again. They reported that as the magic bullet for their problem. I had my father remove and re-seat the battery (I was doing all of this remotely.) Magic! Everything worked normally again. Perhaps there was some sort of static electricity buildup causing problems. Truly bizarre.