Q: iMac suddenly won't Airplay to AppleTV

21.5-inch, Late 2013 iMac 10.9.2

Newest generation Apple TV with latest update installed.

I use to be able to Airplay my iMac screen to my Apple TV. Suddenly, today, for no reason, it won't work.

When I send it from my iMac to the apple tv, it's just a black screen on the apple tv. nothing else. on my imac it says it's on 'extend desktop', but on extend desktop, my wallpaper usually shows up on the apple tv. plus, no matter where i move windows and programs, they never show up on the apple tv. it remains just black and blank.

my imac shows me i have an option to 'mirror screen' but everytime i click it, it closes out of the dropdown menu from airplay on the task bar on the top of the imac screen, and when i open it back up, it's still checked on 'extend desktop'.

but it says 'connected to apple tv' and even gives me the option to 'disconnect from apple tv' so i know it's doing something, and it's giving a black screen on the apple tv, so it's trying to do something, but it's just not working.

i've made sure my imac, apple tv, and my apple wifi router are fully updated, and i also tried turning all of them off and on again (apple tv, imac, wifi router, and cable modem)

the airplay works just fine on my iphone and ipad though, so i don't know what's going on.

posted this on the apple tv forum and they directed me to here.