I cannot access to my own server hosted on my computer with external IP

I need some suggestions and help for this incident. I used to connect my server with external IP for 3 weeks, since it was created. But today I cannot access, only with internal IP. However other people can access as usual with external IP. Do you know what can be the root cause of this issue?
Thanks a lot.

You say it has been possible before.
So I have to assume all firewall and NAT rules are set correctly.
Are you sure the external IP did not change?
Are you sure the server is actually running?
Have you tried restarting the server?

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