Windows Vista Update

how do i fix my windows defender?

my windows defender doesn't work.. Ive contacted HP and Microsoft and they couldn't help..

I tried to download windows defender and re-install it and it said that windows defender was already installed on my computer then shut down.

When i try to launch windows defender a window pops up that says : "Application failed to initialize 0x800106ba.

A problem caused this program's service to stop. To start service, restart your computer or search Help and Support for how to start service manually."

Ive done both my windows defender hasnt worked in months.. when i try to re-install it a box pops up saying "You do not need to install this software because windows defender is included in windows vista.

You can access windows defender from the security section of the windows control panel" but when i try to run it from the windows control panel it still says "Application failed to initialize 0x800106ba.

A problem caused this program's service to stop. To start service, restart your computer or search Help and Support for how to start service manually."

so no matter how hard i try to figure out whats wrong and to fix it... it never works.

Ive tried anything and everything and nothing worked. how do i fix that???