Check your bluetooth, can you use that? If your wifi/bluetooth is grayed out you can do the following; (Warning: If done incorrectly you can destroy your phone.)
Dissasemble your phone, take out the motherboard. Locate the wifi/bluetooth chip and remove the black tape covering it. The chip should look like this; (http://i1.ytimg.com/vi/N3Nn59ZJmyM/maxre...)
Use the smallest heating tool you have at your disposal to warm up the chip along the edges. Ensure you spread the warmth evenly to avoid any damage. Note, the chip needs to get hot. Avoid warming other parts of the phone! If you only have something like a large heat gun or a blow dryer I'd suggest covering the surrounding parts of the motherboard with some kind of heat protection, such as tinfoil.
Allow the motherboard to cool off.
Reassemble your phone.
I've fixed this problem 4-5times using this method. The first time I did was very crude, with a large heat gun. The second time I pulled out a smaller tool, used mainly for soldering allowing me to direct the heat to the wifi/bluetooh chip and that chip alone.