I have UE50RU7400 TV that I bought 2 months ago. I bought a new 4K Firestick and all was OK until a couple of weeks later. The same problem persists where the spinning circle appears, the Firestick logo then appears for a few seconds and then the screen goes blank. I tried the stick in different port with tried the supplied lead and direct into the port. I have also tried different USB port and plugged into AC with the supplied plug and lead.
I first thought this was the stick, but I'm now on my 3rd one from Amazon. I started rebooting the stick and also pulling out the stick from the TV, which is inconvenient as the TV is on the wall.
Now I do t get beyond the initial logo and black screen. I take the stick out, go upstairs to my old TV and the stick works fine. The menu is very clunky and laggy when this problem is going on.