Remove it from Windows' startup list. To do that, go to Run and type in msconfig. Then find it on the Startup tab of msconfig and uncheck the Windows Defender item.
That was my first thought but if it was there is must have been under a ficticius title. The final resolution was Buying and using MalwareRemovalBot. RegVac did not get it but I am wondering if another of your programs would have taken care of it.
I was thinking of Windows Defender and not Windows PC Defender. Windows PC Defender is a program that claims to be an antivirus program but actually puts viruses on your computer. You can do a search online for Windows PC Defender and find removal instructions for it. Here is one page I found - http://www.2-spyware.com/remove-windows-pc-defender.html. None of our programs deal with viruses and so none would take care of it.