1. Many antivirus (Norton, Kap for example) block the internet as they expire (or the date/time is wrong) just to be safe.
2. If it is a bug, try Grif's post at http://forums.cnet.com/7726-6132_102-5098912.html?tag=posts;msg5099421
Remember that such failures are caused by some thousand problems so I can't list them all.
So recently at home my computer has been acting slower than usual. It is a dell inspiron 530 which is hooked up to our Motorola SBV5121XM cable modem. On this computer you can not access certain website such as google, youtube, and a variety of other random sites which usually have a search feature (I am stuck using lycos). Also these same sites cannot be accessed on any devices that are connected to the internet via WiFi on this entire network (iPads, cell phones, laptops). When I try to ping these sites the requests usually time out. I am trying to figure out if this is a network or a computer bug. If someone can please help me, let me know what diagnostics to put up and please let me know what I can try. Thank you!