Thank you for your answers, jdMorgan and mikesz (sorry for my belated answer, I was travelling).
With your approval/experience that Skype is the issue, I made some research on their website and found following solution - which worked for me (I just couldn't believe that I can't use both application - nowadays):
"Conflicts with applications (such as Apache or IIS) working on port 80/443. If you have IIS/Apache or similar software installed that uses ports 80 and/or 443 and you experience conflicts (such as service startup failure or malfunctions) the cause is most likely that your Skype is configured to use the same ports as the applications that experience problems.
There are two possible solutions to this issue:
* In Skype under Tools -> Options -> Connections untick the option "Use ports 80 and 443 for incoming connections". Skype will then use the port specified in the text box (make sure you also have opened that specific port in your router or firewall).
* Configure your http service/IIS/other to use another port for communications"