Helpcannot port forward

i need help with port forwarding at first time i can make minecraft classic server with port forwarding but when i turn it off and turn it on dont work any more
i try to insert port 25565 but it changes to 0 automaticly.

if you know how to fix that pls tell me.
i am using siol modem (prospero 632)
srry for my bad english

Restart your computer. When you close a server like that, sometimes the port will get locked in using the server you just closed, and wont work. Restart your computer and run the server again and it should work.

@Jailbroken671 This also needs to be moved to the Help section.