I haven't had server issues today, but I run a remote VPS. Another option is your router assigned IP for the PC with your server running a new IP Address. I don't know about your port forwarding on your router, but I have to hard-code my IP address for port forwarding. So if my router decides that my PC is now 192.168.1.3 instead of 192.168.1.2 then all my port forwarding will break.
Other than that I'm not sure why it would just stop working.
Success!!! Sweet thanks for the post! I didn't think about the possibility that my extra PC might jump from one IP to another. For the past month I've connected to the server via 192.168.1.2:50500, I just tried connecting with the local IP 192.168.1.3:50500 and it worked. Whats interesting is that when I log into my router as an admin and check out my minecraft custom service I can see that the Start Port and End Port is set to 50500, and the Server IP Address is still set to 192.168.1.2
Quick question, I haven't tested an external connection yet (my GF's PC is on my lan network). Will my friends who connect to my server by using my IP address (different from the 192.168...) connect without any problems since this was an internal lan IP router issue and my external IP address hasn't changed?