Didn't work. It's never that easy for me. The command prompt said it couldn't find the file, so I went in and found it but it had .old at the end. I treid to delete it but it said the file was in use so I turned off updates, rebooted and deleted it but as I said no good. I found an update fixit tool that showed some details, looked at it and it said some components were configured wrong and a file location had changed, it said it fixed it. I rebooted and tried fixit again and said the same thing again several times now. My computer still won't open the diagcab file for the update diagnostic tool. It shows it as an internet explorer file. I used a zip program to unzip it in a folder but I didn't see any .exe file or anything I recognize as a starter file in the decompressed diagcab folder.
This all started a couple of months ago when security essentials dissappeared and defender and firewall came back. Then defender window went blank and can't do anything with it, still shows it running in task manager. I contacted support but nothing they said helped (as usual). Any other ideas? It all seems to be based on .diagcab registry and/or file corruption.