Being able to connect to your Mac but not your PC implies that the firewall or anti-virus on your PC was blocking CC connecting to calibre. So, my first question: which machine do you want to use? We can try to make the PC work if you wish.
As for not being able to connect to the Mac today: could you send me a CC debug log? To do that, start CC, go to Settings, scroll to the bottom and choose "Send a debug log to MultiPie". Please erase the multipie.co.uk email address (my son) while leaving the other one (me). I am working with you so there is no reason to disturb my son.
