Hi.
Does this problem occur only for web surfing? Do you use Safari (compass needle) or have you tried in FireFox or Opera as well?
In Safari, Firefox and other browsers, under the application menu there is an option to Empty out cache. You should try that first, then close Safari (Safari -> Quit) and reopen it. You can also try to "Reset" Safari. You won't lose bookmarks, but it will reset the preferences. Similar things in other browsers.
If that doesn't help, then the first thing you should try to do is go to Finder and /Applications/Utilities (Shift+cmd+U) and run Disk Utility. Make it first check permissions and then attempt to repair them. If that doesn't help, try to check the disk as well. You should restart (turn off/on normally) your Mac inbetween the permission fix and the disk check.
Let us know now this goes?