Why does my wifi say no internet accsess although there is still a connection to the wifi?

When I am playing World of Warcraft of on the net, my internet sometimes randomly disconnects. I am still connected to my Wireless but there is no Internet connection which is confusing. This had happened to my friend when she came over my house and now its happening on my laptop. Anyone have any ideas why the internet would disconnect me, though it is still connected to my wi fi? When i reconnect it once again returns ot a working state.