ios 10.9.5 airplay doesn't work; only tone, no view

Hello,

after a while I wanted to use my apple tv 2 again for mirroring my imac to my lcd tv. in past that worked fine, but today after i installed apple tv only sound was available, but screen stays black. so i updated both engines to the latest versions:

Imac to ios 10.9.5 and my modell is from mid 2011 and airplay worked before

and apple tv to 7.0.3

with iphone 5s, 4s or ipad mini i can do mirror screens easily but from mac i cannot push mirror. extend screen is actually selected and i cannot change

what do i have to do?

by the way i tried also to install a logitech wireless keyboard k750 for mac but the usb unified plug is not recognized but works with other computer.

thanks