Unplug your router/wifi device and let it sit for about 8 min. and then plug it back in.
Then: 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.
Then, if still a problem: Try a soft-reset. Close all apps then - Hold down the HOME, bottom button, and the SLEEP, top button, for about 10 seconds until the Apple icon appears. Allow it to reboot, it may take a few minutes, don't panic like I did, wait for it to reboot. Cures many weird problems on iOS devices.