The first problem is difficult to diagnose. There are a number of factors. For me, the usual suspect is a firewall routing issue.
You see, my firewall requires me to specifically point to an IP for which to route connections from a port.
In the 192.168.x.x range. Sometimes this changes unexpectedly causing connection issues, even on a local level. If you have to manually forward ports (especially if it's directly on the router) this is something to check. You can get the information for this from the Command Prompt. Open it up and type: "ipconfig /all"
Assuming you're on a desktop connection this will be listed under an Ethernet connection. The IP you want is the IPv4 Address, it will say something like this "192.168.0.4 (Preferred)" of course, this varies from computer to computer.
LAN IP for incoming connections in firewall rules.
The second issue, if you're connecting 2 computers in the same house to a server also hosted in the same house. Well, the first problems solution also comes into play here. See, that LAN IP for the firewall rule is actually the IP of which computer receives the inbound information.
So, if you're on the same network, then you can enter that LAN IP from any computer connected to the network and it should connect without any IP conflict.
Remember, localhost and 127.0.0.1 only work when the server host and the client are at the SAME terminal. If they are JUST sharing the same NETWORK, then this doesn't work.