Try changing the Channel number in the Router's wireless settings to see if the new Laptop then finds your "wireless network". The other computers will automatically adjust to the altered channel number.
The default settings are usually either "6" or "11" so try these or, if already using one of these, try the other. Avoid channels 12 & 13, which in some countries are illegal, as some Wireless Network adapters are designed not to connect on these channels. Also avoid 1 & 2 which are used by too many other "wireless" devices, such as mobile/cordless phones etc.