Can you smell burning? If yes one of the capacitors may have blown. On mine I turned it on it's back and open the catch. Then undo the two screws holding a metal plate and you should then be able to open it further and move the plastic cover out of the way. You should then see the circuit and possibly a blown capacitor. If it is that you can just replace the capacitor. Hope that helps.

I know this is a bit late! But, when replacing my 5S battery I broke the wifi antenna (I hadn't realised it initially). I could connect to wifi 5ghz but it was very intermittent and I couldn't get a stable connection plus the 2.5ghz connections just wouldn't work or accept a password. Replacing the Wifi antenna restored everything.