Faults like this can be tricky to diagnose at a distance. The first thing to check would be whether another device (someone else's phone, for instance) can connect. If so, it's a laptop issue and the first port of call would be to delete the network and set it up again. If not, contact the Social Media team on Facebook or Twitter and ask then to check there's no restriction on your account (I don't know whether there's a fair use limit on tethering on unlimited contracts, for instance).
