My wifi is completely greyed out and I can't turn my wifi on. How do I fix it?

I've tried resetting it and everything but it is still greyed out. Ive notice this happened last time a couple days after I updated my softerware and wasn't working for about a month and a half. Then one day it just started working again until I updated my ipod again and now the same thing is happening. My wifi greyed out. How do I fix it?