I can't turn on the Wi-Fi on my iPhone 4S?

It's greyed out and I can't turn it back on! I tried everything resetting network settings
and restoring iPhone but nothing works! I'm currently running iOS 6.1.3. The iPhone is a sprint one.

Try resetting the network settings and rebooting. Restoring, especially as new

Have you tried the complete restore or a hard reset? May be that would work better. Or just call up the executives over there.