Restart the router, if you use a site to much your ISP will block it connecting for a day or so, for example, excessive use on Redtube and it wont connect, but i dont have these problems as my DNS and DHCP come from the servers i run in my attic (Network project )
First I've heard of ISP's doing this?
Also your DNS will be forwarding your requests to a proper DNS server (usually your ISP's or other known DNS if you set it up correctly, otherwise you might be using root hints) yours will just host the local network DNS records.