iOS Settings, General, ResetIf you can’t connect to a wireless network, and you know your userid and password are good, try powering down your device and robooting.

As a last resort, you can Reset your iOS device’s network settings:

  • Tap Settings > General > Reset > Reset Network Settings

Note: This will also reset all your Wi-Fi networks and passwords, cellular settings, and VPN settings.

Reference: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network: