|lol, the question is SIMPLE. Is there a way to detect something that's blocking a port.|
Likewise i havn't seen a program, cmd line, or any other way that's widley known to accomplish what you're asking for OP, other than hit & miss.
I too have ports that i need to open, however, it's not firewalls, service provider, or other obvious software that's blocking these ports.
It's likely something from the computer that's blocking these ports.