Here's what happened: I shut down from Start menu, as you do, the screen went dark for a couple of seconds, and it came back again. I tried that a few times, then tried Restart option with the same result. Ctr+Alt+Del didn't show anything "no response" mark on, so I had to type them twice to restart.... in order to shut down!
It only happened a few times, and as far as I can tell, there's no common cause. It seems to happen at randam, and can be quite annoying, especially it was 12.30am and I wanted to go to bed!
Any help will be welcomed.
Thanks in advance.