In order to work on the largest user base possible (who often are behind routers and firewalls), Skype will listen on port 80 and prevent IIS (and other services) from using it. That may cause some minutes of frustration as your IIS stops working, Visual Studio won’t bind to the local web server, and you repeatedly click “Start” in IIS Manager to no effect.

To put Skype in its place and make it stay away from port 80 for good, open up Skype and go to Tools->Options, General, click “Set connection parameters and proxies”, and uncheck “Use port 80 & 443 as alternatives for incoming connections.” Then restart Skype. That should allow IIS to use port 80 as it needs to.

However, if Skype then stops working for you, you may need to open up a port in your router. You’ll find the port that Skype’s using on the same options page where you unchecked “use port 80…”.