How do you unblock Skype?

Skype

I'm unsure what you mean by unblocking Skype. I can only assume that you need to know what ports Skype uses to set up a firewall to accept incomming calls.

If this is the case then if you open Skype and go to 'Options' on the Connections Tab, the ports currently in use are listed there.

You then need to enter these ports to allow incoming and outgoing connections TCP/UDP in your firewall program. Since I you did not specify the program you are using I cannot instruct you further.