AutoProtect? Umm... a little more detail please?
I'm going to ASSUME you mean AutoProtect in Norton Anti-Virus? If so then either something glitched Norton or you have a virus that snuck through and disabled Norton (first thing most viruses do when they infect you is disable you AV app).
Go to Symantec's site and search their knowledgebase. They have an extensive one and they definately cover this.
My suggestion would be to perform a Live Update and download ALL updates (not just the definitions). May fix the problem only because if you haven't done it in a while, a full Live Update will upgrade your NAV core files.
Also check your startups in MSCONFIG. If you've done some tweaking you may have inadvertantly disabled an NAV app that needs to load on startup (there's usually several of them).
There are also a couple of Norton services. Make sure they're setup to start automatically and not disabled.
You should run a FULL virus scan in SAFE MODE to make sure there's no viruses on your system (make sure you update NAV first).
All else fails you may need to uninstall and re-install NAV.
Optionally you can uninstall NAV and use Grisoft's free AVG which works very well and a lot less code-bloated than Norton. The free AntiVir also works well.
Hope this helps...