Help!!

I have had my computer over a year now and Defender seems to always be turning itself off. I run Windows Onecare with no other programs and Defender is never on. Is this normal, or is there a problem? I turn it on and update/scan and when it is done the next time I shut down it turns itself off and doesn't restart. I have never had any security issues, so far. Any help would be great!

Did you disable that using msconfig ?