I guess that you mean that the laptop can't see the Home Hub's SSID i.e. BTHomeHub-xxxx?
If that is the case it is usually down to being too far away - 50 metres or three regular walls or combination of. Alternatively it is often caused by another device swamping the signal e.g. a wireless AV sender or similar. It can also be caused by neighborers' wireless networks - the cure for which is to change channels on the Home Hub.
t, January 2008