My issue was that my S3 would connect to the wifi and show up as connected but
I still couldn't access the internet or youtube. It would work fine at a friends house.
I followed Mikey23's advice exactly. The only thing I changed was the galaxy S3 advanced wifi setting (DHCP to static + DNS1 and DNS2 to whatever my router showed). I did not need to modify router settings. Note, you still have to re-add the gateway, ip etc. (took me a while to figure that). Did the trick for me.