First, make sure you uninstall the Bing bar from Control Panel-Programs and Features. Then follow the instructions in the link below. It might be a good idea to read the entire thread if it doesn't fix it.
Hope this helps.
This is a HP pavilion d4790y with a new install of vista business 4 days ago. Three days ago, massive amount of up-dates installed including windows live, Internet explorer up-dates. I install Mozilla FireFox, with google as my search engine. I have no Bing toolbars, no bing add-ons, and no MSN toolbars. There was a bing search box in the internet explorer header. Yesterday, any search i did in firefox (google),came back with a bing header. The same with Internet explorer (google), comes back with a bing header. Please help my get rid of bing from my computer.