iPhone 4S crashed, Wifi crashed, Personal Hotspot gone My iPhone 4S, which i got in October, just crashed out of the blue and wouldn't restart.

After reading other people's blogs I managed to restart by holding the main button and on/off button together.

When it rebooted, the wifi and personal hotspots were greyed out and therefore could not connect to the internet. After switching the phone on and off, the wifi reconnected but the Personal Hotspot is still greyed out.

Where has my Personal Hotspot gone and how do I reconnect it?
Since there wasn't physical trauma, you should try to restore its factory settings through iTunes.

You can try to restore your backup afterwards (iTunes will ask you if you want to or use the phone as a new iPhone), and see if it's still working. That should bring back your Personal Hotspot.

If not, re-restore it and set it up as a new iPhone. You'll lost your messages and some settings. But you should be able to keep your contacts (if sync through iCloud, Gmail, or other), and your mails.

If it's still not working, bring it back to an Apple Store, they'll most likely give you a new one.

Since the Personal Hotspot feature is controlled by your carrier, so you might also want to check with them if it's still activated on your account.