Fix DNS Problems

Sometimes when you can't connect to a web site, the cause is a DNS problem. There are things you can do to solve these problems, though. If you're having trouble connecting, to find out if DNS is a potential culprit first ping the site to which you can't connect, by issuing the ping command like this at the command prompt or Run box, like this:
ping www.zdnet.com
If the site is live, you'll get an answer like this:
Pinging www.zdnet.com [206.16.6.252] with 32 bytes of data:

Reply from 206.16.6.252: bytes=32 time=119ms TTL=242
Reply from 206.16.6.252: bytes=32 time=79ms TTL=242
Reply from 206.16.6.252: bytes=32 time=80ms TTL=242
Reply from 206.16.6.252: bytes=32 time=101ms TTL=242

Ping statistics for 206.16.6.252:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 79ms, Maximum = 119ms, Average = 94ms
If it's not, you'll get a response like this:
Ping request could not find host. Please check the name and try again.
If you ping a site and it's live, but you can't connect to it with your browser, a DNS problem might be the reason. If you suspect you're having a DNS problem, take the following actions:
Check your HOSTS file. If your HOSTS file contains an incorrect or outdated listing, you won't be able to connect. Even if you don't recall adding listings to a HOSTS file, it still may contain listings, because some Internet accelerator utilities edit them without telling you. Open your HOSTS file with Notepad and see if the site you can't connect to is listed there. If it is, delete the entry, and you should be able to connect.
Check your DNS settings. Make sure your DNS settings are correct for your ISP or network. Find out from your ISP or network administrator what yours are supposed to be. Then, to find out your current DNS settings, double-click on the problem connection in the Network Connections folder, choose Support → Details, look at the bottom of the tab to find your DNS servers. If they don't match what they're supposed to be, right-click on the problem connection and choose Properties. Then, highlight Internet Protocol (TCP/IP) and choose Properties. Change the DNS servers to the proper ones, or choose "Obtain DNS server address automatically" if your ISP or network administrator tells you to.
Flush your DNS cache. The problem may be related to your DNS cache, so flush it out. To flush the cache, type ipconfig /flushdns at a command prompt.
Find out if your ISP is having DNS problems. The cause may be your ISP. One possibility is that one of its DNS servers is down, and you're trying to access the down server. Ping each of your ISP's DNS servers and, if any of them don't respond, remove them from your DNS list, as outlined earlier in this POST