Need help!

I am running a completely Vanilla Minecraft server, with a port forwarded for it.
It's been running like a charm, but when I got home today, I was unable to join. I looked on the console, and others had been able to log on. My client, however, merely stayed pinging for about 5 minutes, then would say at last that it couldn't connect.
This never happened to me before now. Any suggestions?