Win8 64-bit Pro. Windows Defender Service is running but when I try to run Windows Defender app to bring up the control panel for it I get: "An error ocurred in the program during initialization..... error code 0x80073b01 No other anti-virus installed. I was troubleshooting a slow browsing issue and using some of the Sys Internal tools to turn off some registry settings to try to isolate what service or device was causing the problem. It ended up being that I forgot I had put the computer into power saving mode so it was throttling back the CPU. Anyway, I turned everything back on and then that is when I started having the problem. The Defender App launched fine prior. These are the services that I have left as disabled: Family Safety (tried turning it on, made no difference) Net.Tcp Port sharing Remote Registry Routing and Remote Access Smart Card Smart Card Removal Policy SNMP Trap Storage Service Windows Connect Now Windows Media Player Network Sharing The Windows Defender Service starts and stops just fine. It's just that I can't launch the Security Center (Windows Defender) app. Sys Internals Autoruns is showing everything is checked (enabled) except the following in the Task Scheduler section of the registry settings listing: \Microsoft\Windows\.NET Framework\.NET Framework NGEN v4.0.30319 64 Critical Microsoft .NET Runtime Execution Engine Microsoft Corporation c:\windows\system32\mscoree.dll \Microsoft\Windows\.NET Framework\.NET Framework NGEN v4.0.30319 Critical Microsoft .NET Runtime Execution Engine Microsoft Corporation c:\windows\system32\mscoree.dll (Note there are two other NGEN entries above these two that ARE checked) \Microsoft\Windows\CertificateServicesClient\UserTask-Roam DIMS Job DLL Microsoft Corporation c:\windows\system32\dimsjob.dll \Microsoft\Windows\DiskDiagnostic\Microsoft-Windows-DiskDiagnosticResolver Windows Disk Diagnostic User Resolver Microsoft Corporation c:\windows\system32\dfdwiz.exe \Microsoft\Windows\IME\SQM data sender Microsoft IME 2012 Microsoft Corporation c:\windows\system32\ime\shared\imecfm.dll \Microsoft\Windows\PerfTrack\BackgroundConfigSurveyor Microsoft Performance PerfTrack Microsoft Corporation c:\windows\system32\perftrack.dll \Microsoft\Windows\SideShow\SessionAgent Microsoft Windows SideShow services Microsoft Corporation c:\windows\system32\auxiliarydisplayservices.dll \Microsoft\Windows\SideShow\SystemDataProviders Microsoft Windows SideShow services Microsoft Corporation c:\windows\system32\auxiliarydisplayservices.dll \Microsoft\Windows\SoftwareProtectionPlatform\SvcRestartTaskLogon Software Protection Platform Client Extension Dll Microsoft Corporation c:\windows\system32\sppcext.dll \Microsoft\Windows\SoftwareProtectionPlatform\SvcRestartTaskNetwork Software Protection Platform Client Extension Dll Microsoft Corporation c:\windows\system32\sppcext.dll \Microsoft\Windows\TaskScheduler\Idle Maintenance Maintenance Scheduler Microsoft Corporation c:\windows\system32\msched.dll \Microsoft\Windows\WindowsBackup\ConfigNotification Microsoft® Windows Backup (Not verified) Microsoft Corporation c:\windows\system32\sdclt.exe \Microsoft\Windows\WindowsColorSystem\Calibration Loader Microsoft Color Matching System DLL Microsoft Corporation c:\windows\system32\mscms.dll \Optimize Start Menu Cache Files-S-1-5-21-3026344430-126586880-762360923-1001 twinapi Microsoft Corporation c:\windows\system32\twinapi.dll All other entries displayed by Autoruns are checked on. I initially had Avast anti-virus installed but it had issues with Windows 8. I uninstalled it an enabled Windows Defender. The Windows Defender app (Security Center) ran just fine thereafter. I wasn't until I started changing settings in Autoruns and Services that it broke. Unfortunately I didn't backup the registry. The problem here as I see it is two fold: a) The error message is very ambiguous aside from the error code. An internet search on that error code turns up very very little so it is not a common error. So there is no definitive information as to the specific possible causes. B) Microsoft Security Essentials uses to be a standalone product. So if you had issues you could uninstall and reinstall it. But now that it is "built in" to Windows 8 under the name of "Windows Defender" I see no way to re-install just that component without refreshing the entire system and losing dozens and dozens of desktop apps that took hours and hours to install and configure. Supposedly Lego's install_wim_tweak.exe can remove Defender all together using this command on Windows 8 (): install_wim_tweak.exe /o /c Windows-Defender /r What I need is a command then to reinstall it! Isn't there some sort of DISM command I can issue to reinstall windows defender.?