If the wireless network is working fine, and all the wireless settings on a computer are correct, it may be frustrating if an individual computer still can't receive any wireless signal.
One thing that may be wrong is that computers often have a hardware switch that turns the wireless functionality on or off. Hence, even if the wireless network driver is enabled, the computer will still be unable to locate any wireless signals if this little switch is in the "off" position. Often, the switch can be turned off by accident if someone brushes against the computer.
Here's one useful site for laptop users that gives information on where to look for the wireless switch on different brands of computers, including Acer, Dell, Sony Vaio, Toshiba, and many more: