Windows 2K prof. Sp4 can't update & run defender definition

Hi,
My two computers system is run Windows 2K prof. Sp4. I want to install
defender but failure in update defender definition. It need to install root
cert. firstly (ref. KB924123) that can be solved. Then I go to microsoft
support download to get root cert. by updated web site and select it. It has
shown the installation screen a long time and fail.

- What does this error code mean? [0x800106ba] -error message shown this
service stop!
- Other question is why can't update?
Please help me to solve these problems? Thanks