I had this problem few days before as well, wifi was working fine at my house but when I connected to my cousin's wifi, fone did connect but the wifi signal bars turned grey instead of green and even though I was connected at excellent strength I had no internet connectivity... thought it might have been some settings issue with my cousin's router but when I returned home the situation did not change , still connects to the router but no data at all 
tried many things, rebooting fone, unplugging router, switching in and out of Flight mode,even flashed a different modem on the fone, nothing worked...finally gave up and did a factory reset which is such a PITA as had to backup and restore a ton of stuff....wifi started working normally after factory reset
Then 3 days later, I was browsing through the Filkie Wallpapers HD app when it froze and after a while my fone restarted...lo and behold...the wifi problem was back after the restart...WTF !!! I cant keep hard resetting my fone after every 2 days help me plz....there must be something I can do to fix this
tried many things, rebooting fone, unplugging router, switching in and out of Flight mode,even flashed a different modem on the fone, nothing worked...finally gave up and did a factory reset which is such a PITA as had to backup and restore a ton of stuff....wifi started working normally after factory reset Then 3 days later, I was browsing through the Filkie Wallpapers HD app when it froze and after a while my fone restarted...lo and behold...the wifi problem was back after the restart...WTF !!! I cant keep hard resetting my fone after every 2 days
help me plz....there must be something I can do to fix this