windows defender update issue

seems it wont update windows defender on windows 7. Tried to run Defender and it says explorer.exe cant be found. I think it either isnt there or wont reinstall. tried to update hotfix, sfc /scannow and remove/reinstall defender. any ideas?

After clicking to open Defender, can you post a pic. of the message related to the missing Explorer.exe?

here it is

Anything related to Defender showing up either in the Action Center--> Security, or in the Event Viewer logs shown as critical errors? And how did you go about uninstalling / reinstalling it?

nothing showing up in action center and under security it isnt listed. Tried the files
WindowsDefenderX64.msi. Tried the uninstall. install and repair feature.
Event viewer only showed this for windows update.

Installation Failure: Windows failed to install the following update with error 0x80070643: Definition Update for Windows Defender - KB915597 (Definition 1.77.575.0).

thx.. nm got it, ran sfc again, and was able to fix the screwed up files.. defender works and updates work.