can't seem to authenticate only from windows 7 laptops

Hi, I’m new to the list and freeRADIUS. I’ve encountered a problem while I’m trying to build a wireless network environment using freeRADIUS. I’ve setup a custom wireless router using Openwrt and freeRADIUS with Mysql. I have a couple of wireless clients - smartphones, laptops (win7, win8, mac)

From windows 8 station, mac and smartphones I can access to wireless router successfully authenticating through freeradius, while I can’t seem to authenticate from windows 7 clients.

I’ve checked the error logs from radius server and windows 7 client is sending their computer-name as an username instead of the one I entered. I don’t have any domain controller nor am I using certificate right now. Any suggestion? Thanks, D Kim