As you know, I have had a particularly tricky virus on my PC which, apart from popping up sites all the time, had disabled my ability to restart, shutdown or hibernate my PC.

I tried AVG, Windows Defender and Ad-Aware. None of them got rid of it. Tonight I finally installed Spybot S&D and guess what! It found the little bugger, healed it, and when I re-booted (manually shutting the power off) – the problem is solved. I can shutdown again! Hooray! Thank you Spybot S&D.