My computer does that every once in a while, for no apparent reason. Usually IE is running at the time and is not responsive. I chalk it up to Microsoft, mostly. If you have not done so, download MalwareBytes' Anti-Malware, then reboot and install it and run it in safe mode the frst time. Keep it updated, and run it often. You may have to run it several times at first to help clear things up - I had to run it on my friend's computer at least three times before we got it cleaned up when he was having some real problems! MalwareBytes' web site is here: Malwarebytes.