puters done my tree in

[masha]

tonight fired up the puter and went to go to the forum and it changed back to the start page so i clicked it again got on the forum went to log in and it went back to start page ,after restarting puter a few times patience was wearing thin and a large lump hammer was comming to mind till i thought of the cost ,then i remembered a site i had saved free downloads encyclopedia-softpedia all sorts of stuff to down load ,out went avast anti virus in came comodo anti virus and everything was rosie again ,dont know if anyones using comodo but it seems to have sorted me out p/s anyone know what causes this to happen ???