wifi problems

http://support.apple.com/kb/ts1559

1. Verify that airplane mode is off by tapping Settings > Airplane Mode.
2. Reset the network settings by tapping Settings > General > Reset > Reset Network Settings.
   Note: This will reset all network settings, including Bluetooth pairing records, Wi-Fi passwords, VPN, and APN settings
3. Ensure that your device is using the latest software. To do so, connect your device to your computer and check for updates in iTunes.
4. If your issue is still unresolved, perform a software restore in iTunes.

Additional Information

If you are still unable to turn Wi-Fi on, please contact Apple for support and service options.

Read here:

http://support.apple.com/kb/ts1559

If nothing works, make an appointment at an Apple store.

Did you follow the steps in:

Troubleshooting iOS WiFi

and

WiFi Greyed Out

completely? When resetting the network router you have to disconnect the power completely so the router is shutdown and not in standby mode as many do when the power button is pressed.

If none of this works, backup the iPhone, then reset to factory condition, Settings > General > Reset > Erase all Content and Settings, then restore from the backup. See if that does the trick.

If not, visit an Apple store gemius bar and have it tested by the technicians.

When you go through the Troubleshooting steps, one step is to reset the router...the network wireless machine. When you reset the router, the purpose is for it to get a new IP address from your Internet Service Provider to use as the starting address for your wirelelss network. To do that the router has to be completely powered off, if it is in standby mode it will not get a new starting IP address. Thus, the suggestion to disconnect the power to the router so you are certain it is actually powered off.