Apple TV Screen Flashes after install atv flash AND can't get screen mirroring to work

Hi

I am all new to this and after spending the afternoon with a second hand Apple TV 1st Generation installing atv flash (silver), I am at a loss as to:

  1. Why the screen is now flashing

  2. Why air play does not work. I have installed the Remote HD plug in but my iphone does not recognise Apple TV

Erghhhh Help!

Thanks