A lot of the browser add-ons cause issues, particularly Hotbar......many of my clients have experienced fluky behavior associated with it. Maybe try getting rid of the Yahoo bar and afterwards running Spybot (can be found at download.com- just enter spybot for the search criteria) to clear out any spyware that might be present. A while back my system at home got very bogged down, especially when browsing, and the removal of spyware got it back up to snuff and acting normally.