As a general rule of thumb...use local static IP addresses on ALL wired devicesYou can figure out DNS issues by putting a known WAN IP in your browser (or pinging), like Amazon.com (
http://72.21.206.6/); if you can ping a WAN IP and cannot ping a domain name, then obviously it is a DNS issue.Now, you most likely had a local IP address issue (as mentioned above with 2 or more DHCP servers that over-lapped leased IP addresses). Routers (that are also DHCP servers) should always be set to start leasing addresses at around .50 or .60 and reserve all the DHCP automatic stuff for wireless devices (manually set local IP addresses on all wired devices); and
you should always make sure that only 1 router or Server is a DHCP server.
A good rule of thumb with setting manual IP addresses is to Set all routers to local static IPs of (.1 thru.5), Servers to local IPs of (.6 thru .10), Printers to (.11 thru .20) and workstations/Macs, PCs to .21 thru .31
Also remember to check the Gateway IP address when you manually configure devices (which should match the local IP address of your Internet router (usually 192.168.1.1 or 192.168.0.1) or you will not get out to the Web with 1 bad typo.