Is your system software fully up-to-date with Software Update? If not, now would be a good time to do that and get any detected malware removed at the same time.
Are you using the correct Domain Name Server (DNS) numbers your ISP gave you to look up Internet "phone numbers"? Check them against the ones your ISP says to use, which should be readily available in your ISP help pages. NO valid DNS number begin with 85.xxx.yyy.zzz.
If you are in the US, you can use OpenDNS or Google DNS standard DNS numbers. In South America, Africa, Europe or Asia, these may cause additional delays.