Wifi greyed out on macbook air

Hi All,

My macbook shut down overnight due to some internal error and since restarting the Wifi icon in the top right corner is greyed out. I cannot switch wifi on or off. When I go to Network preferences wifi is not listed down the left hand side menu bar. When I click the + button to add a wifi network, I again don't get the option, only Thunderbolt Bridge, Thunderbolt 1, Bluetooth Pan, VPN, PPPoE or 6to4. Has anyone else had this problem? And what is the fix? Is one of these options what I need to set up wifi?

Perplexed!

Thanks

Katie