I have a similar issue from time to time. For some reason when it happens to me, it says my connection is secured with WEP (its actually WPA2) and it wont let me connect to it or the open "guest" signal from my router either. Sometimes turning off wifi and turning it back on again helps, other times I just have to wait. The other night it went on for a couple of hours. No idea what the cause or solution is though.
This is first Android phone and I'm beginning to wonder if it was a mistake. I upgraded to it because of the large bright screen, WiFi & 4G connectablity among other things. During the first 10 days of use I used 65% of my 200Mb limit and had to upgrade to 2Gb. I was told to do a hard reset of the phone and the setup the WiFi before installing any other apps, however that didn't work. The FoxNews app doesn't work and the Weather Channel app crashes when I try to view the radar map. I'm thinking about rooting the phone but I'm very concerned about bricking it. I wonder if it is a hardware issue?