Can't access my multiplayer minecraft server on a different computer?

You have to port forward, or the server is not up in your terminal... I can only help on MACS for port forwarding... can ANYONE access it besides you from YOUR computer? Also, your IP could have changed (if you port forwarded, you have to do it again)

and.. What is the error message on it?

How to Port Forward on a Mac

Go to 192.168.1.1 which is your router's page. You will have to type a username and password. The username is probably ADMIN. You then have to open NETWORK PREFERENCES and look at the IP It should be 192.168.1.???. Click on PORT FORWARD or GAMING in your menu on the router page... It should say Port Forward... Type in the IP that you saw in network prefrences (the last 2 or 3 numbers) in the end of the port forward thing. Make the ports 25565. Save. Go to ipchicken.com The IP that shows up there is the one you type in in your Minecraft Server Connect..

Hope This Helps!