Everything was working fine yesterday, but this morning when I walked in only a computer that was in my firewalls DMZ was able to locate the server. None of the other computers can resolve the FQDN of the server and attempting to ping the IP returns timed out. When I attempt to ping any device on the intranet, the server returnes with "General Error"
Could be a physical or data link layer problem. I've had switches that failed overnight to auto-negotiate a link speed and provided a half on-half off kind of connection (24 port Linksys Gbit switch). Causes very weird problems.
If you can load websites that aren't cached, your server is obviously able to use its routing table, and takes you through some gateway (all 0.0.0.0/0 routes will be used for that purpose by your server) to transfer data. Also, this proves that some form of DNS is working. Unless you have a proxy server set up, in which case that server will do all the work for you.
Not being able to ping your gateway from different computer would mean that the gateway could have a problem.
Also, don't forget: if you have a DHCP server or client messing up, you could possibly have an IP address conflict, those can be VERY hard to diagnose. Check for this. I have a Seagate GoFlex Home network attached drive that somehow manages to get the wrong ip-address assigned every single time.