Just in the last 2 days, we are getting the message that a DNS error occurred. Have tried the fixes already out here, but still not working. Only happens on certain sites, such as Facebook.

We have a LAN setup and recently had problems with our server. Since we had someone in to fix the server, we now cannot get to certain websites such as Facebook. The message is OOPS Link appears to be broken. DNS error occurred. Server cannot be found. We did the fix regarding the prefetch, checked firewall settings. We have not loaded any new programs, etc. The only updates may have been the Microsoft automatic updates since we do that when rebooting and we had to reboot multiple times while the server was being fixed. Anyone out there help? I'm missing my Facebook.  : ) Thanks.