wifi could not turn on after updating ios 6.1.3

Fix for Personal Hotspot Missing After iOS Update
We?ve heard from a few readers in our comments and through emails that after updating to iOS their Personal Hotspot disappeared on the iPhone. The reason for this is unclear, but thankfully the fix is extremely easy:

• Open Settings and tap on ?General?
• Tap on ?Reset Network Settings?

Now tap back to Settings and you should see the familiar Personal Hotspot option. Yes, you will lose your wireless network passwords and custom DNS settings by resetting network preferences, so be sure to note any necessary network settings before doing so.
Strangely enough, the same Personal Hotspot disappearance happened with some users who updated to iOS too, so presumably it may even happen in the future with yet another iOS update. Why? It?s probably a bug, but it?s so easy to fix it?s not that big a deal.
Tethering is still not working?
Another possible fix is to retype the access point name in through Internet Tethering (Personal Hotspot) settings. This can be accessed through Settings > General > Network > Cellular Data, look under ?Internet Tethering? for APN, and fill in an access point name. A username and password are not required. Note in iOS 6 and newer, ?Network? is now labeled as ?Cellular? in settings.

Personal Hotspot Still Missing? Try This

Another common issue with Personal Hotspot disappearing after an iPhone update is that it simply gets turned off on it?s own. This sometimes requires either to be re-activated or just set up again. Why that happens is not entirely clear, but it?s super easy to turn back on:

• Open Settings, go to General, then go to Cellular (or Network)
• Scroll all the way to to the bottom and look for ?Personal Hotspot?, it may appear as ?Set Up Personal Hotspot? if the setting was tossed out
• Re-activate Personal Hotspot through there, then go back to the primary Settings menu to find Personal Hotspot available again
•  Post a Question....