Setting a password to connect to WIFI


Hi,I have ZTE wifi modem. One of my laptops have problem in connecting with the modem with security. When i remove the security and make it open, it connects easily. All other laptops, mobiles have no problem even when security is on. I think the problem is with the laptops wifi driver, tried everything but not sorted yet.Now, i want to make it open network but still want that modem should ask for password. Is there any way to do this? I have kept the modem pppoe mode and don't want to change this.Also can i get any manual for the modem. Model is ZTE ZXDSL 531B.thanks.