This is a well known issue with windows 7; surprised to hear that you're having problems with windows 8 which as yet hasn't affected my main (windows 8)pc. I had this 2 or 3 times with my windows 8 laptop and the problem was caused by a the personal profile info stored by windows becoming corrupt. The only thing that I could put it down to at the time was that I was in the habit of closing the laptop lid BEFORE it had finished closing down. I found that the only real time saving way to sort it out was to back up everything important and then re-install etc. Since I got in the habit of allowing my laptop to close down properly before closing the lid I haven't had this issue for about 8-9 months now. Not saying that this is what has caused your problems; but I've had no problems since then.Hope this helps- and good luck!!