I have the same problem as listed in this question, briefly, when I try to install Cygwin I have empty list of sites. (BTW the Cygwin mirrors site works fine from my browser!)
The problem I know is due to the K9 filter I have installed.
I tired whatever K9 advises to disable the filter per this link but I can only install Cygwin when K9 is completely uninstalled.
Any suggestions how to have K9 and install Cygwin ?
Thanks!