Remove all toolbars-they are a front for keystroke and other types of spies. Not sure how many you have. Got to start-go to search and type toolbar and start search. I found a friends computer was running slow with about 100 toolbars. His was extremely slow.
Use your spybot or whatever to remove crap.
Tools-options-delete all cookies.
Use your av program-then if nothing use an outside av check. Use trendmicro/housecalls. Works extremely well.
Also look at your modem and check for activity-watch the activity lights to see for action. While on your desktop, there should be no activity. If there is, you have something running. You need to find and stop it-except for av programs of course.