Hi, I have a question reguarding winsock connection.

In some cases, when certain people try to connect to my server they never reach or make a connection request on my side yet on their side it says that it didn't find the server.

I use www.no-ip.com so they always have my current IP address, also i've tried editing my no-ip.com account so that they connect to other reasonable IPs that I currently have... and still they are not able to connect to me.
Is there a reason why they cannot reach/find me and can this be fixed?

Thanx