Go to a command prompt and do an nslookup on the wget target node name, e.g., "nslookup (insert FQDN here)". If nslookup is not installed, you may need to install the DNS utilities package.
nslookup should return either the IP address of the target node, or a fairly verbose error detailing why the lookup failed.
Case 1: wget throws an error, nslookup does not: Something fishy is going on if nslookup correctly resolves the IP address but wget claims it can not. Please post a session log.
Case 2: wget throws an error, nslookup does not: There is an issue in DNS resolution in the host system that must be corrected before wget will work.