You need to provide what browser you are using!
One fist common thing is to clear your browser cache. Puhaps you also should clear your cookis cacheĀ“if you got many cookies in it that you dont need. Remeber that some cookies have your autologin for some sites so you need to know all login to those sites befre you clear your cookies.
If you using IE 8 or 9 you can also clear the checkbox for "Save information about your favorit wab places" that collect some information that normaly is unnessesary. Check also your accelerators if you have to many of them activated without using them.
Check also if you have toolbars that you are not using installed in your system.
Run a manual virus check on your system so you know that you have no virus. You can also use the SPybot to particular check your Web browser for virus and other malware. That is free to use for home users.
http://www.safer-networking.org/