Can't get laptop to connect to 4S WiFi hotspot

I apologize if this has already been asked but I just can't explain why my laptop (Dell XPS) won't connect to my brand new 4S over WiFi.

I'm trying to use the phone as a modem. Even though personal hotspot is enabled on the phone, sometimes my laptop's WiFi adapter will not find the iPhone at all. Other times it will. But the interesting thing is that when it does, it connects for like a second and then the connection is dropped by the iPhone. I even tried to use my older 3GS. Initially it connected to the 4S and the indicator icon on the 3GS changed to hotspot. But after a second, the connection was dropped.

So I'm thinking that it's not my computer or but the 4S itself. I checked with my carrier and they do allow that kind of connection.