It is most likely that a program that you use has added a lot of entries into the winnt/system32/drivers/hosts file. This file basically contains a list of rules for various websites and is commonly added to by ad blocking software. I had this same problem with linkshare.com and the 404 errors and this was the trick. You must leave the localhost entry (127.0.0.1) for your computer to function and I highly recommend backing up the hosts file before playing with it as it is important to your system.
Good luck and hope this helps...I know it drove me crazy until I found out the secret.