First step is to connect using the supplied yellow ethernet cable and verify your broadband connection is working that way, and then log into the routers interface to confirm that the wireless network is turned on and what it is called.
Some computers/devices do have wireless driver problems, particularly I've found with the HomeHub 3, and you may need to turn off the wireless N part of the router, i.e. run it in the older B and G mode.
The HH3 is meant to seek out the least congested frequency, and I do wonder whether it is this that at times causes problems.
Software like http://www.netstumbler.com/
can be run and will reveal what wireless networks are visible to a computer, even if you are not actually able to use them.