I was using Firefox to browse videos on youtube when my computer became quite unresponsive with stuttered mouse control and a stuttered beep coming from the speakers, almost like the system was overloaded. There is no way my system was overloaded with the tasks I was running, I know my computer quite well and can usually trace problems, but this, I have never seen before: When I pressed ctrl-alt-del to bring up task manager and find out what the smeg was happening, it went to the blue options screen i.e. the one you can choose to start task manager or log off etc, but instead of options I got a message saying "Starting Task manager Security". Quick as a flash I power off and remove network cable and re-boot. But there is nothing that I can see in the event log except for my forced power off.
Are you sure it was "Stating Task Manager Security" or was it "Preparing Security Option"/
This screen is shown if the CPU usage is high and the computer performs slowly and has to display this message. On other occassions, the computer is so fast that this message gets skipped.