Guest laptops connect but have no data transfer.

I will assume you have setup your router and changed some basic settings and are using some sort of security on your wirelss router, WEP, WPA, etc. I have had this problem in the past where the security settings were not just right and it showed connection, but not activity. I had changed from WEP to WPA and a family memeber who previously could connect could not anymore.

On you friends laptop, delete the the profile for your router and start over. ie. find your router and add it to their laptop with the current password. Do not just try and change it, as it can still give you issues.

Another possiblity is you have turned on "Wireless Card Access List", MAC filtering. This could also allow a person to connect but then not allow data transfer.

Beware: Before you hold the reset button for over 5 sec, as another suggested, you will be defaulting your router to new out of the box settings with no security or any previous modifications.

Unplug the cable modem, wait 10 secs and plug it back in. Do the same for the router. if no luck, reset the router with the reset button behind by holding it down for 15 secs and release, then wait 60 secs and try connecting again. If no luck, its something to do with the internet settings on your friend's laptop.