It might be an incorrectly configured DNS, in the settings for the NIC, click on the advanced button to make sure there is nothing listed causing an issue. Also, you could change your DNS provider to someone like OpenDNS. (126.96.36.199 and 188.8.131.52) I've had pretty good luck (and speed) out of using OpenDNS rather than an ISP's DNS. If your local DNS is glitchy, being attacked, or down you could have DNS issues. Also, Google has DNS @ 184.108.40.206 that anyone can use.