Well if skype still works when this happens, you are still connected to the Internet.
Here's a couple of suggestions. It could be your firewall blocking port 81 every so often or more than likely its something to do with the domain name service.
Domain name service (dns) is a server which converts addresses we use such as 'yahoo.com' into the servers address so the computer can recognise the address. Computer communicate with ip address such as 192.168.1.28 (dns) allows us to type in the address and it converts it for us.
If your computer is configured to assign you an dynamic IP address then it automatically assigns you to your isp's dns server. I'm thinking when so many computer connect to the router, it conflicts with the dns. Without dns functioning, you cant surf the web.
You could set up a static ip and use a open dns to stop the conflict. Before you do that, next time you have this problem do this.
start> run> type cmd and press enter. On the prompt screen type ping "yahoo.com" without the quotes but make sure there is a space between ping and yahoo.
If it ping that means you can connect to the yahoo server so the problem is with the dns server. If it doesn't ping then you cant connect and could be a firewall problem blocking http port 81. To confirm its port 81, when it happens again send an email as emails use a different port.
If you can send emails its definitely a prob with port 81. If you cant then its something more than just the firewall.
Hope this makes a tad of sense to you lol.