Windows Defender Failed To Start

[tree_fu_go]

I had this problem for a while but ignored it.

So I was told to disable Windows Defender because it would conflict with my current Antivirus (Avast free) but when I try to open it in control panel it says:

Application failed to initialize: 0x800106ba. A problem cause this

program's service to stop. To start the service, restart your computer or

search Help and Support for how to start a service manually.

What does this mean, does it mean Windows Defender isn't running and I should leave it or is there a problem?

Because of this, I've been not updating Windows (Just the Windows Defender definitions) in case it messes up my computer or something.

I've got Windows Vista 32-Bit, Avast 7 free (I know, I know, theres an Avast 8...), Malwarebytes free.

Thanks, and sorry for making so much topics all the time... >_>

[tree_fu_go]

Okay, Im sorry for bumping but I've been not updating the definitions for Windows Defender incase it wrecked my computer because Windows Defender can't start. I don't know I'm im still suppose to update the definitions or not.