Hello suave_finesse and welcome to Geeks to Go,
I need a little additional information to ascertain whether or not I will be able to assist you, in correcting your problem.
Please Answer the following questions:
1) What operating System's do you have on the PC's in question, Please include any Windows Updates or Patches (Example... XP SP1 or 2)?
2) What is the Model and Manufacturer of the Wireless Adapter currently Installed on your problematic PC?
3) What is the Model and Manufacturer of the Wireless Router you are using?
4) Are you using the software that came with your wireless adapter to manage your connectivity to the router, or if using XP are you using the Wireless Zero Configuration (referred to as WZC)?
5) What IP Configuration are you using (Example.. DHCP, PPoE / Static, Automatic)
6) What troubleshooting steps have you taken already?