Error 0x80070005 | MSE | Can’t Install Microsoft Security Essentials
If you are trying to install Microsoft Security Essentials and you get error code 0x80070005 the first thing you should look for is an existing installation folder. There is a good chance that the trusted installer does not have permission to delete or overwrite some of these files. Typically I just delete the following folders if they exist and then I rerun the MSE setup program. In many cases that solves the problem.
C:\Program Files\Microsoft Security Client
C:\Documents and Settings\All Users\Application Data\Microsoft\Microsoft Security Client
C:\Documents and Settings\All Users\Application Data\Microsoft\Microsoft Antimalware
If that doesn’t work then you can run Sysinternals Process Monitor, exclude everything except setup and find the file, folder, or registry key that is showing with the result of “access denied”. Fix the access denied issue and Microsoft Security Essentials should install or you might advance to a new error code.
For Error 0x80070645 | MSE | Can’t Install Microsoft Security Essentials
Backup your registry and then delete these registry keys. You should have one of them depending on your OS:
Good luck and let me know in the comments if this solved your problem.