Try this, go into SETTINGS - GENERAL - NETWORK, then chose the line with your network name on it and then press the blue arrow on the right, then tap the FORGET THIS NETWORK button at the top of the page. Then setup your network again. OR, you can try to tap RENEW LEASE and see it that helps. The first option above is the best one to try, as it resets everything in the network settings. This worked for me when I had a low signal two foot from the wireless router and could not connect.
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Also, reset your WiFi/ router by unplugging it for about 8 min, and then plugging it back in.
If that doesn't work, go back into the setup page and tap the DNS address field, it will probably have something like 192.168.1, (remember what's listed there) listed on it, change this to (Google public DNS server) 8.8.8.8 and see it that helps. If not put back the original DNS address.