Laptop can't connect to public Wi-Fi?

My Lenovo laptop connects fine to my Wi-Fi at home but I have strange problems with it at college when trying to connect to their Wi-Fi.

Sometimes I can go a whole day without having any problems with the internet but most days I can only connect for about 1 minute before I lose connection.

Anything I can do? I have tried lots of stuff including firewalls and I'm using Windows 7.

Its probably not your computer, its the router/AP at the college or public place. This happens at my college too.