I repeat: Do a defrag.
Run antivirus in safe mode, and an anti spyware too, perhaps Malwarebytes, http://www.malwarebytes.org/
Question: Can you remember when this started?
I've recently noticed that more and more problems happen because unwanted programs get installed as attachments to programs one downloads and installs, and they are not necessarily noticed by security programs - I had four of them myself, causing pop-ups, not noted by security, but they had to be uninstalled. You might do a service to yourself by checking if you have some "unknown" installations, lately. Control Panel\All Control Panel Items\Programs and Features, click the "Installed on" so that you get the latest installation first.
Hope you get it working.