My wifi button has greyed out on 3gs

Hi MayankHanda,

Welcome to Apple Support Communities!

Take a look at the article below, it provides the possible resolutions to the issue you described.

iOS: Wi-Fi settings grayed out or dim

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

In rare instances, the setting to turn on Wi-Fi on your iPhone, iPad, or iPod touch may appear grayed out or dim. You might see the following when you tap Settings > Wi-Fi.

If this occurs, your device won't respond when you try to turn Wi-Fi on. If you're using iOS 7.1, "Wi-Fi Not Available" might appear in Control Center.

Resolution

Follow these steps to resolve the issue:

1. Restart your iOS device.
2. Make sure that airplane mode is off by tapping Settings > Airplane Mode.
3. Reset the network settings by tapping Settings > General > Reset > Reset Network Settings.
   This will reset all network settings, including Bluetooth pairing records, Wi-Fi passwords, VPN, and APN settings.
4. Make sure that your device is using the latest software. To do so, connect your device to your computer and check for updates in iTunes.

If you still can't turn Wi-Fi on, please contact Apple for support and service options. If you can turn Wi-Fi on but are experiencing other issues with Wi-Fi, see how to resolve those Wi-Fi issues.

-Jason