Windows Defender services stop and the defender fails to start after KB3118754.. I have tried to start the services manually and every other trick in the book, no luck. I have no other Anti Virus running on this computer (in case of conflict) and I have also tried registry edits as well as the gpedit.msc fix (Turn off Windows Defender (Disabled)), no chance.. I have tried looking and fixing errors, and a complete Windows upgrade in place!!), to no avail. All other Windows 10 installations are running well (apart from random intermittent issues), I am convinced that Windows 10 B10586 is still unfinished product and that Microsoft will soon issue a fixes that don't say what are they fixing. In the mean time, I will try another in place Windows 10 upgrade, before a fresh clean install. I don't know about other users' experience, but it seems that installations on MBR partitions don't exhibit as many "critical" problems as the GPT ones (I cannot substantiate this due to not enough testing).. One other useful peace of information: During my struggle to resolve this issue, I tried the instruction: Dism /Online /Cleanup-Image /RestoreHealth /Source:esd:F:\sources\install.esd:1 /limitaccess But I kept getting "Access Denied", Now I suspected it is a syntax issue, so I tried every combination I could come up with.. surprisingly, DISM /Online /Cleanup-Image /RestoreHealth /source:ESD:F:\Sources\Install.esd:1 /LimitAccess gave me a different error; I did not know that Windows instructions were case sensitive!. However, this was not the problem... The problem was that I was double clicking on the ISO image and it would show as drive F: (this would lead to Access Denied in spite of the fact that I could read files inside it). I then right clicked on the ISO image and mounted it, this has worked.