In trying to run a server that listens on port 80 (successfully on Windows XP and Windows 7), I found that the service could not attach to port 80 after I updated to Windows 10. It turns out that, as part of the upgrade, Microsoft has the “World Wide Web Publishing Service (W3SVC)” listen automatically on that port.
The fix: run “services.msc”, stop the World Wide Web Publishing Service (W3SVC), and then change its Startup Type to either “Manual” or “Disabled”.
Thanks go to DeveloperSide.NET for pointing this out!