unusual connection problem

just to get the basics out of the way:

laptop - vista
router - linksys - model: BEFW11S4


i'm having trouble connecting to the internet ONLY when i set the password
for the network. when the network is unsecured, i have no problems with the
connection. however, once i get the password set up, i won't be able to
connect at all. signal strength would be excellent [i'd be 2 feet away from
the router]; and after diagnostics are ran, the advice given is for
"troubleshooting low wireless signal quality problems," which obviously isn't
the case. i had assumed it was because my router was set to block WAN
requests, so i went and disabled that; still not connecting.

i don't know what else to do. any help is greatly appreciated. =]