if you were out of range or the router was turned off, you wouldn't even be seeing it, so you can rules those out.
most likely would be the wireless key, how confident you are entering it correctly?
making sure of case sensitivity and O is for oscar and 0 is for zero and all that.
next would be extra security they have on the wifi router, like MAC filtering.
if enabled, you may need not only a wifi password but to be physically allowed by given them you MAC network address.
but only the administrator of the router can verify, and if needed, add you to the 'allowed' list.