I am afraid i had this same problem I had reinstalled windows and everything was running fine for around 5 months I then installed spybot on the recommendation from a friend and after several crashes and hangs and numerous strange errors it finally happened i was unable to login to windows, I tried several fixes from this site and google but to no avail, in the end, I had to do a repair install to fix it I have since stopped using spybot and have had no further errors. Windows defender and nod32 appear to do the trick I have had no hangs which i used to get whilst running spybot and also have had next to no popups, no viruses ever and my pc has run smoother than ever since removing spybot, if it is very cpu intensive as i have read on this site then that is not a good thing in my mind. good luck