I can't get my wifi on its grey

Try the suggestions here to see if they resolve your problem:

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

If these don't work you may have a hardware problem. Visit an Apple store for an evaluation or contact Apple Support.

I have the same problem - it worked fine up until I updated to 6.1.2 over the weekend, now wifi is deactivated. I've done all those things suggested in the link, but nothing has fixed it. I find it hard to believe that wifi (which has always toiled away unobtrusively without so much as a blip) should suddenly croak at the same time as an undate 'fixing' a wifi glitch in iOS. Especially since I don't seem to be the only person to be having this problem. I guess I'll have to give Apple a call tomorrow.

If anyone finds a workaround - please post it. I'd love to know what the problem is rather than having to replace the Wifi hardware.

I tried the overheat suggestion someone else made after no luck on an old iPhone 4s - put the hairdryer on the phone until warning came on, let phone cool down, turned off and then when turned back on, it worked! May have to do a networks reset, but had done that before trying the heating option. May not last, but it is working now!