Web server not accessible to other systems on LAN

I'm trying to test a web site being served via nginx on my Mac. Things work just fine accessing the server on that same Mac, but when I try to get to it from a couple of Windows machines on the same WAN via the Mac's IP address, I can never get further than "This page cannot be displayed." I'm pretty sure this used to work…

Both using IE and Telnet on the Windows machines to try to get to my server is failing. However, if I turn on Windows sharing in the Network pane of OS X's System Preferences, I can access the filesystem, so I know that it's not that my entire Mac is inaccessible.

I thought it might be a firewall thing, but I checked and confirmed that my wifi router doesn't have its firewall enabled. OS X has a firewall, but nginx has a hole poked in it, and completely disabling the OS X firewall doesn't help anything at any rate.

On my Mac, I can see that nothing is being added to either nginx's error or access logs when I try to access the server from the Windows machines, so I assume whatever is failing is happening in the network layer.

I'm a networking newbie and at a loss of what to try next. Any tips on what to try next would be appreciated.