Is this a virus?

Recently when I start up my computer my start up configurations have been altered and everything is turned on. Our computer was running incredibly slow so I ran some virus scans and they were coming up with no virus found. So next I checked the start up configurations and sure enough every box was checked. I unchecked them all, applied, restarted and everything was fine. a few days later..... same thing. What could be messing with my system start up configurations?
Thanks