Cannot access to Internet

Hello, Windows XP Desktop is showing that its connected to the internet, but when I try to open internet explorer it says. Cannot Find Server. Page can not be displayed. How do I get it to connect? My laptop is wired to a router thats
connected to my desktop and the internet on there works fine. For some reason though just the internet on my Desktop does not work. I also hooked my internet directly to my laptop and it works fine. But still my desktop is showing the same thing. I recently tried to Install Windows Service Pack 3 and there was a problem. It said Access Denied then quit the Installation. Since then I am not able to access the Internet. Does anyone know how to fix this? If so please let me know thanks.